UC-NRLF 


C    3    Dbb    fl32 


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GIFT  OF 

Charles  L.   Camp 


yy 


OW  LEDGE. 


Y  S  T  E  M 


N  S. 


D. 


[ACCEPTED   FOB   PUBLICATION,  MAT,   1852.] 


VOL.    V. 


ART.  4. 


PROFESSOR   JEFFRIES    WYMAN. 


SKETCH  OF  DR.  JEFFRIES  WYMAN. 


355 


a  brandling  tree.  These  buds,  no  doubt,  make  you  think  of  something 
you  have  seen  before — the  yeast -babies — yes,  these  are  the  baby- 
li'/ilriv.  Soon  their  lingers  begin  to  grow;  then  they  loosen  them- 
selves from  the  old  mother  hydra,  and  begin  to  "  fish  for  themselves." 
The  next  time  you  go  wading,  you  must  try  and  capture  some  of  these 


—  Old  hydra. 


Feelers,  or  tentacles. 


Young  bydrse. 


FIG.  42. — OLD  HTDKA  AND  YOUNG  ONES. 


wonderful  little  creatures,  and  see  if  you  can  find  all  that  I  have  de- 
scribed without  my  help.  You  are  now,  I  trust,  opening  your  eyes 
to  the  great  world  of  living  things  all  around  you,  in  whi.^i  y6U  have! 
lived  and  played,  as  I  lived  and  played — blindfolded.  AjicJ, 
once  your  eyes  are  really  open,  wide,  there  is  no  toljing 
they  may  behold. 


OW  LEDGE. 


Y  S  T  E  M 


SKETCH  OF  DR.  JEFFEIES  WTMAK 

BY  BURT  G.  WILDER, 

PROFESSOR   OF   ZOOLOGY  IN   CORNELL   UNIVERSITY. 

WITHIN  a  year,  science  has  lost  two  of  her  greatest  leaders,  Louis 
Agassiz  and  Jeffries  Wyman.  With  the  life,  the  works,  and 
the  appearance  of  the  one,  all  are  familiar.  But  the  other  was  hardly 
known  outside  of  strictly  scientific  circles.  He  rarely  gave  popular 
lectures,  and  never  wrote  any  thing  that  attracted  general  attention. 
Yet  his  influence  upon  the  progress  of  science  in  this  country  has  been 
very  great,  and  he  had  for  years  been  regarded  by  all  as  the  highest 
anatomical  authority  in  America,  and  the  compeer  of  Owen,  Huxley, 
and  Gegenbauer,  in  the  Old  World. 

JEFFRIES  WYMAN  was  born  at  Chelmsford,  near  Lowell,  Massachu- 
setts, August  11,  1814.     His  father  was  a  physician,  as  is  his  surviv- 


N  S. 


D. 


[ACCEPTED   FOB   PCHHCATIOU,   MAY,   18  52.] 


VOL.    V. 


ART.   4. 


356 


THE  POPULAR   SCIElfCE  MONTHLY. 


ing  brother.  II.-  was  prepared  for  college  at  Phillips  (Exeter)  Acad- 
emy, entered  Harvard  University  in  1829,  and  was  there  graduated. 
During  his  last  year  in  college  he  had  an  attack  of  pneumonia,  which 
nearly  proved  fa'tal;  this  doubtless  predisposed  him  to  the  pulmonary 
weakness  from  which  he  suffered  during  the  latter  part  of  his  life,  and 
from  which  he  died  on  the  4th  of  September,  1874,  at  Bethlehem,  New 
Hampshire. 

Soon  after  his  graduation  he  entered  the  Harvard  Medical  School, 
and  in  1836,  became  "house  medical  student"  in  the  Massachusetts 
General  Hospital. 

In  1837  he  received  the  degree  of  M.  D.  His  graduation  thesis 
was  upon  the  eye,  and  accompanied  by  drawings.  It  does  not  appear 
to  have  been  published,  but,  in  September  of  the  same  year,  the  Bos- 
ton Medical  and  Surgical  Journal  contained  a  paper  by  him  upon  the 
"  Indistinctness  of  Images  formed  by  Oblique  Hays  of  Light."  Soon  - 
afterward  he  became  Demonstrator  of  Anatomy  in  the  Medical  School 
under  Prof.  J.  C.  Warren,  whose  chair  he  was  destined  afterward 

to  fill. 

In  1839  he  accepted  the  curatorship  of  the  newly-founded  Lowell 

Institute.     Two  years  later  he  delivered  therein  his  first  course  of 

public  lectures  (of  which  no  report  has  come  under  our  notice),  and 

with  the  money  .so  earned  went  abroad  for  a  year  to  pursue  his  medi- 

"vsal  ai\d/8p»aftifif  studies  under  the  great  European  masters.     He  had 

''already,  since' V83S,  published,  in  the  American  Journal  of  Science, 

•  si<yfera1l)3rie£pjtpe.r»upon  anatomical  and  physiological  matters. 

'  l*n  l&43*there  were  published,  in  the  Journal  of  the  Boston  Soci>  ty 
of  Natural  History,  anatomical  descriptions  of  two  gasteropod  mol- 
lusks  (Tebennophorus  Carolinensis  and  Glandina  truncata).  Like- 
wise a  paper  on  the  chimpanzee  (Troglodytes  niger),  in  which,  with 
characteristic  modesty,  his  account  of  its  organization  (though  sub- 
versive of  some  of  Owen's  previous  conclusions)  is  subordinated  to 
Dr.  Savage's  remarks  upon  its  habits  and  external  characters.  The 
same  year  he  was  appointed  Professor  of  Anatomy  in  the  Hampton- 
Sidney  Medical  College,  at  Richmond,  Virginia.  During  his  four  years' 
stay  his  contributions  to  science  included  some  notes  upon  fossil  re- 
mains of  vertebrates,  and  longer  papers  upon  the  blind  fish  of  the 
Mammoth  Cave  and  the  teeth  of  the  gar-pike  (Lepidosteus).  The 
latter  paper  is  illustrated  by  microscopic  sections,  showing  the  closu 
resemblance  of  the  gar-pike's  teeth  to  those  of  the  fossil  batrachian 
Labyrinthodon.  The  article  closes  with  the  suggestion  that  some  of 
the  separate  teeth  then  referred  by  Owen  to  the  latter  genus  might 
really  belong  to  Lepidostean  forms.  This  paper  alone,  though  little 
known  and  never  quoted  by  its  author,  would  serve  to  show  what 
manner  of  man  was  rising  in  America. 

In  1847,  at  the  age  of  thirty-three,  he  was  chosen  to  the  Hersey 
Professorship  of  Anatomy,  at  Cambridge.    The  year  of  his  inaugura- 


SKETCH   OF  DR.  JEFFRIES    WYMAN.  357 

tion  was  signalized  by  his  account  of  the  gorilla,  based  upon  speci- 
mens forwarded  to  him  by  Dr.  Savage.  This  was  the  first  scientific 
description  of  the  new  Troglodytes. 

From  that  time  forward  his  scientific  progress  was  rapid  and  un- 
broken. He  collected,  he  investigated,  he  lectured,  he  wrote.  His  0  W  L  E  D  G  E 
admirable  course  of  lectures  upon  Comparative  Physiology,  before 
the  Lowell  Institute,  in  1849  (the  report  of  which  in  pamphlet  form 
has  long  been  out  of  print),  soon  caused  him  to  be  regarded  as  the 
foremost  among  American  anatomists  and  physiologists. 

During  this  .period,  and  indeed  until  within  a  few  years  of  his  death, 
Prof.  Wyman  published  frequent  brief  notices  of  new  animals,  of  points 
of  structure  and  function,  the  value  of  which  is  in  no  way  to  be  meas- 
ured by  their  length.  Almost  any  one  of  them  would  have  served  a 
less  modest  man  for  an  extended  memoir,  while  several  contain  the  ele- 
ments of  interesting  popular  articles.  So  far  from  this,  Prof.  Wyman 
seemed  to  attach  little  personal  importance  to  them,  rarely  referred  to 
them,  or  took  any  pains  to  have  them  reproduced  elsewhere.  Many 
were,  however,  copied  into  European  journals. 

His  first  extended  paper  was  "  On  the  Nervous  System  of  Rana 
pipiens  "  (the  bull-frog).  It  covers  fifty  quarto  pages,  with  two 
plates,  was  published  by  the  Smithsonian  Institution  in  1853,  and 

should  be  in  the  hands  of  every  student  of  either  human  or  compara-  "V"     tt  "p1     TV/I" 

tive  anatomy,  as  the  clearest  introduction  to  the  most  complex  of  ani- 
mal structures. 

Somewhat  similar  to  the  last,  not  quite  so  long,  but  even  more  re- 
plete with  fact  and  philosophy,  is  the  "Observations  on  the  Develop- 
ment of  Raia  batis"  (a  skate),  published  by  the  American  Academy  of 
Arts  and  Sciences  in  1864.  This  was  based  upon  few  materials,  but 
sufficed  to  convince  him,  and  all  naturalists,  that  the  skate  ranks 
higher  than  the  shark,  since  the  latter  retains  through  life  a  general 
form  resembling  one  of  the  stages  through  which  the  former  passes 
during  its  development.  Vj"  O 

Those  who  knew  Wyman's  nature  may  well  imagine  how  he  shrank  1- '      O  • 

from  any  thing  like  a  discussion  of  two  great  questions  upon  which  so 
much  has  been  written  during  the  past  fifteen  years,  namely,  the 
"  Origin  of  Species  "  and  "  Spontaneous  Generation."  But,  aside  from 
his  natural  desire  to  know  and  teach  the  most  correct  doctrine  upon 
these  subjects,  his  prominent  position  made  it  imperative  that  he 
should  consider  them  carefully.  Respecting  evolution,  he  evidently 
felt,  -with  Prof.  Gray,  that,  "  upon  very  many  questions,  a  truly  wise 
man  remains  long  in  a  state  of  neither  belief  nor  unbelief;  but  your  -pv 

intellectually  short-sighted  people  are  apt  to  be  preternaturally  clear- 
sighted, and  to  find  their  way  very  quickly  to  one  or  the  other  side 
,  of  every  mooted  question."  In  1863  he  wrote  as  follows  :  "  We  must 
either  assume,  on  the  one  hand,  that  living  organisms  commenced 
their  existence  fully  formed,  and  by  processes  not  in  accordance  with 


[ACCEPTED  FOB   PUBLICATION,  MAY,   1852.] 


VOL.    V.  ART.   4. 


358 


THE  POPULAR   SCIHM'H   MOXTHLY. 


the  usual  order  of  Nature,  as  it  is  revealed  to  human  minds,  or,  on  the 
other  baud,  that  each  species  became  such  by  progressive  development 
or  transmutation;  that,  as  in  the  individual,  so  in  the  aggregate  of 
races,  the  simple  forms  were  not  only  the  precursors,  but  the  progeni- 
tors of  the  complex  ones,  and  that  thus  the  order  of  Nature,  as  com- 
monly manifest  in  her  works,  was  maintained." 

No  one  can  help  seeing  that  he  inclined  toward  belief  in  the  gen- 
eral doctrine,  but  he  neither  indorses  "  Darwinism "  nor  denounces 
those  who  find  themselves  unable  to  accept  "  derivation "  in  any 
sense. 

Regarding  the  appearance  of  organisms  de  novo,  he  never  allowed 
himself  to  express  a  final  opinion.  He  published  two  papers  embody- 
ing the  results  of  numerous  and  accurate  experiments,  and,  we  have 
reason  to  know,  was  still  continuing  his  observations  at  the  time  of 
his  death. 

The  general  question  to  which  Prof.  "Wyman  gave  most  attention, 
until  called  from  it  by  the  Archaeological  Museum,  was  that  of  Organic 
Symmetry,  especially  as  manifested  in  the  limbs.  Accepting  the  usual 
belief  in  an  homology  of  the  front  and  hind  limbs,  he  associated  there- 
with the  idea  first  put  forth  by  Oken,  that  the  two  ends  of  the  body 
are  symmetrical,  or  reversed  repetitions  of  each  other,  as  are  the  right 
and  left  sides.  The  application  of  this  doctrine  to  the  limbs  makes 
the  ulna  the  homologue  of  the  tibia,  the  radius  of  the  fibula,  and  the 
thumb  of  the  little-toe,  instead  of  the  great-toe,  as  ordinarily  be- 
lieved. 

So  radically  does  this  interpretation  of  "  intermembral  homologies  " 
differ  from  that  of  most  anatomists,  that  it  is  not  strange  that  its  ac- 
ceptance is,  at  present,  confined  to  a  very  few  (Foltz,  in  France,  and, 
in  this  country,  Dana,  Coues,  Folsom,  and  the  writer).  But  we  are 
encouraged  by  the  reflection  that  our  leader  never  gave  even  a  quali- 
fied assent  to  any  doctrine  which  did  not  prove  to  be  in  the  main 
correct. 

Upon  no  other  single  problem  did  he  bestow  so  much  thought. 
And,  as  may  be  inferred,  it  is  in  his  treatment  of  this  question  that 
his  peculiar  characteristics  appear.  In  the  adoption  of  new  ideas  he 
manifested  a  wise  caution,  which,  contrasted  with  the  haste  of  others 
less  well  informed,  illustrates  the  maxim,  "  Fools  rush  in  where  angels 
fear  to  tread."  We  recall  his  freedom  in  discussion  with  his  students 
and  his  kindness  in  aiding  their  advancement,  even  to  his  own  appar- 
ent detriment ;  his  modesty,  occasioning  a  lack  of  reference  to  his 
own  papers  or  to  unpublished  investigations  ;  his  critical  acumen, 
which  was  the  more  searching  and  useful  from  its  entire  freedom  from 
personality ;  and,  finally,  here  shine  forth  in  their  greatest  brilliancy 
those  rare  qualities  which  enabled  him,  when  occasion  required,  to 
overlook  the  delusive  charms  of  teleology,  though  upheld  by  popular 
interest  and  theological  authority,  and  to  regard  her  plainer  but  more 


SKETCH   OF  DR.  JEFFRIES    WYMAN.  359 

reliable  sister,  morphology,  supported  by  relative  position  and  mode 
of  development. 

In  1866  Prof.  Wymau  was  named  one  of  the  seven  trustees  of  the 
Peabody  Museum  of  American  Archaeology  and  Ethnology,  and  be- 
came curator.  For  this  work  he  was  peculiarly  fitted,  both  by  nature 
and  by  his  extensive  observations  upon  crania,  and  his  frequent  in- 
vestigations of  shell-heaps,  etc.,  during  the  trips  to  Florida,  which  his 
health  had  of  late  years  forced  him  to  make.  Our  space  will  not  per- 
mit even  a  brief  sketch  of  his  labors  in  this  new  field  ;  the  results  are 
modestly  recorded  in  his  annual  reports.  At  present,  the  Museum  is 
very  extensive  and  admirably  arranged.  Had  Prof.  Wyman  been 
spared  lor  another  ten  years,  one  can  hardly  predict  its  importance. 
Of  this,  and  of  his  own  anatomical  collections,  the  value  is  wholly  out 
of  proportion  to  the  size  or  actual  cost  in  money,  for  they  represent 
the  constant  and  skillful  labor  of  a  great  anatomist  during  a  quarter 
of  a  century.  The  label  upon  every  specimen  tells  the  truth  so  far  as 
he  knew  it ;  and  in  the  descriptive  catalogues  are  rich  treasures  of 
fact  and  thought  as  yet  unrevealed. 

Prof.  Wyman  always  shrank  from  public  notice,  and  from  posi- 
tions in  which  this  was  involved.  He  attended  several  meetings  of 
the  American  Association  for  the  Advancement  of  Science,  and  served 

therein  as  president,  treasurer,  and  secretary.    But  his  communications  "XT     CJ     TT\    T7 

were  few,  and  comparatively  unimportant.     He  was  a  member  of  the  JL      O     _L     JLd 

American  Academy  of  Arts  and  Sciences,  and  was  named  by  Con- 
gress one  of  the  original  fifty  members  of  the  National  Academy  of 
Science,  but  soon  resigned.  In  strong  contrast  with  his  slender  rela- 
tions with  these  organizations  is  his  record  in  connection  with  the  Bos- 
ton Society  of  Natural  History.  He  early  became  an  ardent  member, 
served  as  secretary,  and  as  curator  of  several  departments,  and  in  1856 
became  president.  This  office  he  held  until  1870,  when  he  offered  an 
unqualified  resignation. 

Meagre  as  is  the  above  account  of  his  outer  life,  we  shrink  yet  more  J.\| 

from  any  such  estimate  of  his  abilities  and  his  personal  character  as 
the  present  occasion  will  permit.  Admired  and  trusted  by  his  asso- 
ciates, by  the  younger  naturalists  he  was  absolutely  adored.  Ever 
ready  with  information,  with  counsel  and  encouragement,  so  far  from 
assuming  toward  them  the  attitude  of  a  superior,  he  on  several  occa- 
sions permitted  his  original  observations  to  be  more  or  less  merged 
within  their  productions.  The  universal  regard  in  which  he  was  held 
by  them  is,  in  the  writer's  case,  intensified  by  the  sense  of  peculiar  -p. 

obligations,  which  might  cloud  his  judgment  of  any  ordinary  man ; 
but  to  no  man  more  fitly  than  to  Wyman  could  be  addressed  the  lines : 

"  None  knew  thee  but  to  love  thee, 
Nor  named  thee  but  to  praise." 


[ACCEPTED   FOR    PIMILICATION,  MAY,   1852.] 


VOL'    V"  ART.   4. 


360 


THE  POPULAR   SCIENCE  MONTHLY. 


Nor  was  any  criticism  ever  made  upon  him,  from  any  quarter,  other 
than  upon  his  extraordinary  freedom  from  personal  ambition,  and  his 
aversion  to  public  notice  or  display. 

Wyman's  anatomical  work  was  absolutely  free  from  zoological 
bias,  and  his  statements  were  always  received  as  gospel  by  both  par- 
ties to  a  controversy.  He  might  not  tell  the  whole  truth,  for  he  mitrht 
not  see  it  at  the  time ;  but  what  he  did  tell  was  "  nothing  but  the 
truth  "  so  far  as  it  went.  The  hottest  partisan  felt  that  a  figure  or 
description  of  Wyman's  was,  so  far  as  it  went,  as  trustworthy  as  Na- 
ture herself. 

Without  brilliancy,  Dr.  Wymau  combined  qualities  rarely  found 
in  the  same  individual.  No  man  of  our  time  has  surpassed  him  in 
the  love  of  Nature  for  its  own  sake,  free  from  the  hope  of  position, 
power,  or  profit ;  in  keenness  of  vision,  both  physical  and  mental ;  in 
absolute  integrity,  with  the  least  as  well  as  the  greatest  things;  in 
industry  and  perseverance;  and  in  method,  whether  for  the  arrange- 
ment of  collections,  or  the  presentation  of  an  idea.  And  if  to  these 
had  been  adjoined  a  tithe  of  the  ambition  displayed  by  smaller  men, 
and  had  his  health  and  strength  been  at  all  equal  to  his  mental 
powers,  no  one  can  doubt  that  his  attainments,  his  productions,  and 
his  reputation,  would  have  been  surpassed  by  none  of  his  contem- 
poraries. 

However  much  we  may,  for  our  own  sakes,  regret  that  such  was 
not  the  case,  we  know  that  into  his  mind  never  entered  the  shadow 
of  bitterness.  His  recognition  of  others'  labors  was  full  and  generous  ; 
his  mind  was  upon  the  facts  and  principles  of  Nature,  and  regarded 
not  the  medium  through  which  they  were  obtained ;  and  if  he  ever 
prayed  for  health  and  strength,  it  was  surely  not  for  his  own  advance- 
ment, but  because  he  felt  within  himself  the  desire  and  the  ability  to 
learn  and  to  teach  the  truth. 

Dr.  Wyman's  reputation  was  less  wide  than  that  of  some  others ; 
but  it  was  deeply  rooted.  As  the  years  roll  on,  and  as  the  final  esti- 
mate is  made  of  the  value  of  what  has  been  done  in  this  century,  we 
may  be  sure  that  the  name  of  Jeffries  Wyman  will  stand  high  among 
those  who  have  joined  rare  ability  and  unwearied  industry  with  a 
pure  and  noble  life.  To  use  his  own  words  upon  a  like  occasion, 
"Let  us  cherish  his  memory  and  profit  by  his  example." 


SMITHSONIAN    CONTRIBUTIONS    TO    KNOWLEDGE. 


ANATOMY 


THE    NERVOUS     SYSTEM 


OF 


RAN  A    PIPIENS. 


BY 


JEFFRIES  WYMAN,  M.  D. 


[ACCEPTED  FOB   PUBLICATION,  MAY,   1852. 


VOL.    V.  ART.   4. 


COMMISSION 


TO     WHICH    THIS     PAPER     HAS     BEEN     REFERRED. 


J.    B.    S.    JACKSON,    M.   D. 
JOSEPH    LEIDY,    M.   D. 


JOSEPH    HENRY,    Secretary  S.    1. 


CAMBRIDGE: 
HETCALF     AND     COHFAifT, 

PKLMtUS  TO  IUE  U.X1TEB£ITT. 


CONTENTS. 


INTRODUCTION, .... 

SECTION  I.  —  The  Brain,  ....  .... 

Olfactory  Lobes, ... 

Cerebral  Lobes, 

Corpora  Striata, 

Optic  Thalami, 

Pineal  Body,         .  ...  .  •  .         .     11 

Pituitary  Body, 

Optic  Lobes, .12 

Cerebellum,       .... 

SECTION  II.  —  Internal  Structure  of  the  Brain,      .  .  .... 

SECTION  III.  — Spinal  Chord,    . 

SECTION  IV.  —  Peripheral  Portion  of  the  Nervous  System,   .         . 

Olfactory  Nerves,      ...  •  ....  .         • 

Optic  Nerves, ** 

o/» 

Motor  Communis, 

07 
Patheticus, 

Trigeminus,       .  ....  . 

A.  Ophthalmic  or  Orbitar  Branch,  .         .  .  • 

B.  Upper  Maxillary  Branch  and  Abducens, 

C.  Mandibular  or  Lower  Jaw  Branch,    .  .  .29 

D.  Facialis, 

oo 

Auditory  Nerve, 

oo 
Vagus, 

q£ 

Nervus  Lateralis, 

qi-y 

Nervus  Dorsalis, 

SECTION  V.  —  Philosophical  Anatomy  of  the  Cranial  Nerves  and  Skull,        .                 .        .     37 
SECTION  VI.  —  Spinal  Nerves, 

Hypoglossus, "" 

Brachial  Nerves,        .  ... 

Lumbar  Nerves, .        . 

Coccygeal  Nerve, ....  . 

Cutaneous  Branches  of  the  Spinal  Nerves,     . 

Crystal  Capsules  attached  to  the  Spinal  Nerves, 
SECTION  VII.  —  Sympathetic  Nerve,      .         .  .... 


EXPLANATION  OF  THE  PLATES, 


89O41 8 


ERRATA. 

Page  20,  line  25,  for  "detached,"  read  "detected." 

"    23,    "    32,    "    "  Bdelostoma,"  read  "  Bdcllostoma." 
"    44,    "      1,    "    "connected,"  read  "covered." 


ON 


THE    NERYOUS    SYSTEM 


OF 


RANA    PIPIENS,    LIN. 


THE  following  memoir  comprises  an  anatomical  description  of  the  nervous  sys- 
tem of  a  single  species  of  Batrachian  Reptiles,  one  of  the  largest  existing  represent- 
atives of  the  Anourous  group.  The  peripheral  portion  especially  is  described  some- 
what in  detail ;  likewise  some  of  the  changes  which  it  and  the  nervous  centres 
undergo  during  the  process  of  metamorphosis.  A  comparison  is  made  between  the 
temporary  conditions  of  some  of  the  organs,  as  observed  in  the  young,  with  the 
permanent  conditions  found  in  the  class  of  Fishes,  from  which  it  appears  that 
there  exists  a  more  complete  analogy  between  some  of  the  anatomical  condi- 
tions of  this  class  and  the  Iarva3  of  Batrachian  Reptiles,  than  has  been  generally 
recognized. 

In  drawing  up  the  descriptive  details  of  this  memoir,  there  are  many  which  have 
been  already  noticed  in  other  and  allied  Reptiles  ;  nevertheless,  they  are  drawn  from 
a  species  whose  anatomy  has  not  as  yet  been  fully  described,  and  which  in  some 
respects  differs  from  that  of  the  closely  allied  species  ;  it  is  therefore  probable, 
that  the  want  of  agreement  between  the  results  contained  in  this  memoir  and 
those  of  other  anatomists  whose  works  are  quoted,  is  dependent  upon  specific 
differences. 

In  the  details  relating  to  the  cranial  nerves,  there  are  some  facts  noticed,  which 
have  not  only  a  bearing  on  their  physiology,  as  in  the  case  of  the  facial  nerve,  but 
upon  the  philosophical  anatomy  of  the  nervous  system,  and  the  reduction  of  all 
of  the  cranial  nerves,  except  those  connected  with  the  organs  of  the  special  senses, 
to  the  common  spinal  type. 

The  nervous  system  of  Batrachian  Reptiles  is  worthy  the  attention  of  the  anato- 
mist, on  account  of  the  great  simplicity  of  its  structure,  presenting  a  condition  in- 
termediate between  the  two  extremes  of  the  Vertebrate  series,  as  exhibited  by  that 
of  the  higher  Mammals,  on  the  one  hand,  and  that  of  the  Cyclostome  Fishes  and 
2 


6  ON    THE    NERVOUS    SYSTEM  IV. 

Atnphiozus,  on  the  other.  The  spinal  chord  in  the  Anourous  species  exhibits  the 
general  peculiarities  of  the  division,  and  in  addition  the  enlargements  correspond- 
ing with  arras  and  legs ;  while  the  brain  is  so  far  reduced  in  the  relative  proportion 
of  its  different  parts,  and  so  far  stripped  of  the  "  accessory  organs  of  perfection," 
as  to  enable  the  student  to  obtain  with  ease  a  clear  conception  of  the  general  plan,  a 
conception  always  so  difficult  to  acquire  when  studying  the  brain  of  Mammals  or  of 
Man.  In  these,  the  cerebrum  and  cerebellum  so  far  transcend  all  the  other  organs 
of  the  encephalon,  that  the  parts  which  in  a  morphological  point  of  view  are  of 
equal  value  have  been  frequently  overlooked,  as  forming  either  integral  parts  or 
primary  subdivisions.  In  Frogs,  in  common  with  the  lower  Vertebrates,  while  no 
one  part  takes  an  excessive  development,  there  is  at  the  same  time  no  one  of  the 
fundamental  ones  either  wholly  deficient,  or  so  far  reduced  as  to  deprive  the  general 
plan  of  any  of  its  more  important  features. 

In  making  a  dissection  of  the  cerebro-spinal  axis,  when  the  canal  in  which  it  is 
lodged  is  laid  open,  one  of  the  peculiarities  which  first  attracts  the  eye  is  the  ex- 
istence of  a  whitish  substance  deposited  in  a  somewhat  irregular  manner,  but  prin- 
cipally on  the  sides  and  around  the  veins,  extending  through  the  whole  length  of 
the  canal  and  into  the  cranium,  where  it  is  especially  abundant  in  the  neighborhood 
of  the  optic  lobes.  Occasionally  it  will  be  found  in  such  quantities  as  materially 
to  embarrass  the  anatomist  in  his  dissections,  and  at  other  times  only  traces  can  be 
detected.  Under  the  microscope  this  substance  is  resolved  into  vast  numbers  of 
minute  crystalline  forms,  consisting  of  calcareous  matter,  and  similar  to  those  here- 
after to  be  described  in  connection  with  the  spinal  nerves,  where  it  is  found  lodged 
in  peculiar  capsules,  and  in  which  the  quantity  is  more  constant. 

After  the  chord  is  completely  exposed,  one  of  its  most  striking  features,  when  com- 
pared with  the  same  part  in  other  Reptiles,  except  Anourous  Batrachians,  is  its  short- 
ness. (Plate  II.  Fig.  1.).  The  point  at  which  the  last  pair  of  spinal  nerves  is  given 
off  is  just  beyond  the  middle  of  the  trunk,  that  is,  at  about  the  seventh  or  eighth 
dorsal  vertebra.  Beyond  this  the  chord  is  continued  only  in  the  form  of  a  slender 
thread,  which  has  been  compared  to  a  ligament,  though  it  contains  the  microscopic 
elements  of  the  chord,  but  at  the  same  time  giving  off  no  nerves,  and  is  lodged  and 
terminates  in  the  long  and  slender  coccyx.  In  other  Reptiles,  on  the  contrary,  in 
Saurians,  Chelonians,  Ophidians,  and  Urodel  Batrachians,  the  chord  is  continued  as 
such  to  the  extremity  of  the  spinal  canal,  giving  off  its  pairs  of  nerves  nearly  opposite 
to  the  intervertebral  foramina  which  correspond  to  them.  While  it  has  this  excep- 
tional shortness  in  the  adult  of  the  Anourous  species,  it  is  of  great  interest  to  notice 
the  fact,  that,  in  their  embryonic  condition,  they  conform  more  nearly  to  the  general 
rule,  as  was  long  since  shown  by  Serres,*  by  numerous  other  observers  after  him, 
and  as  will  be  seen  in  the  sequel  of  these  pages  ;  nevertheless,  as  will  be  shown 
hereafter,  this  caudal  portion  does  not  conform  precisely  to  the  true  spinal  type. 
The  subdivisions  of  the  central  axis  into  brain  and  spinal  chord,  and  of  these  into 
subordinate  parts,  are  enumerated  in  the  following  tabular  view. 


• 


*  E.  R.  A.  Serres,  Anat.  Comp.  du  Cerveau  dans  les  Quatres  Classes  des  Anim.  Verteb.     Paris, 
1829. 


IV. 


OF    RANA   PIPIENS. 


CENTRAL   AXIS.  — PLATE  1. 


SPINAL  CHORD.  — FIG.  1. 

I.  MEDULLA  OBLONGATA  I. 

II.  BRACHIAL  ENLARGEMENT  L. 

III.  CRURAL  ENLARGEMENT  N. 

IV.  COCCYGEAL  PORTION  0. 


BRAIN. -Tics.  1-9. 

I.  OLFACTORY  LOBES  A. 

II.  CEREBRAL  LOBES  B. 

III.  CORPORA  STRIATA  C. 

IV.  OPTIC  THALAMI  D. 
V.  PINEAL  BODY  E. 

VI.  PITUITARY  BODY  F. 

VII.  OPTIC  LOBES  G. 

VIII.  CEREBELLUM  H. 


With  the  exception  of  the  corpora  striata,  which  are  lodged  and  concealed  in  the 
cavities  of  the  cerebral  lobes,  all  the  parts  above  enumerated  may  be  seen  without 
dissection,  from  a  merely  superficial  examination.  When  stripped  of  their  mem- 
branes, and  examined  in  a  recent  state,  there  is  a  striking  contrast  between  the  brain 
and  chord  as  regards  color  ;  the  first  having  a  grayish  semitransparent,  almost  gelat- 
inous appearance,  whilst  the  second  is  opaque  and  whitish,  the  latter  color,  however, 
being  traceable  to  a  certain  extent  in  the  interior  of  the  cerebral  masses.  Black 
pigment-cells  are  to  be  seen  scattered  over  the  general  surface  of  the  brain  and  spi- 
nal chord,  but  are  especially  abundant  about  the  optic  lobes,  which  are  much  darker 
than  the  cerebral  lobes. 

SECTION  I.  —  THE  BRAIN. 

I.  Olfactory  Lobes.  (Plate  I.  Figs.  1-9,  A.)  —  These  form  the  anterior  por- 
tion of  the  cerebral  mass,  but  are  so  intimately  connected  with  the  cerebral  lobes, 
that  they  might  be  supposed  to  form  with  them  one  and  the  same  pair  of  organs, 
and  have  been  sometimes  described  as  such.  The  only  mark  of  separation  from 
the  cerebral  lobes  is  a  slight  constriction  at  the  line  of  contact,  visible  both  on  the 
under  and  upper  surface,  though  farther  back  in  the  latter  than  in  the  former ;  con- 
sequently, when  seen  from  below,  the  olfactory  lobes  appear  relatively  larger  than 
from  above.  A  condition  of  things  rarely  met  with,  perhaps  only  in  a  few  Anou- 
rous Batrachians,  is  the  fusion  of  the  right  and  left  olfactory  masses,  with  scarce  a 
trace  of  any  indication  that  they  are  double  organs.  In  Toads  they  are  likewise 
fused,  but  are  separate  in  Siren  and  Menobranchus.  (Fig.  5.)  This  union  of  the 
olfactory  lobes,  however,  is  analogous  to  what  occurs  in  the  cerebral  lobes  of  Sharks 
and  other  Plagiostome  Fishes,  and  in  the  optic  lobes  of  the  Lepidosiren,  and  as  it 
seems  in  Menobranchus.  Their  fusion  is  a  subject  of  additional  interest,  since  it 
tends  to  show  that  they  are  developed  from  a  single  embryonic  vesicle,  and  not  from 
a  pair  of  vesicles.  If  this  statement  be  true,  then  we  have  the  olfactory  lobes  ar- 
rested in  their  development,  previous  to  the  division  of  this  vesicle.  An  analogous 
state  of  things  is  easily  shown  in  a  chick  of  the  fourth  day,  where  the  optic  lobes 
form  a  single  vesicle,  though  they  subsequently  become  double  and  widely  sepa- 
rated from  each  other.  In  Lepidosiren,  according  to  Owen,  there  is  but  one  optic 
lobe,  and  that  on  the  median  line ;  we  may  therefore  regard  this  last  as  the  vesicle 


8  ON    nn:  M.RVOUS  SYSTEM  iv. 

undivided.  The  fusion,  or  rather  the  absence  of  separation,  of  the  cerebral  lobes  of 
Plagiostome  Fishes,  is  undoubtedly  to  be  explained  in  the  same  manner. 

It  should  be  remembered  that  the  olfactory  lobes  are  not  represented  in  the  prim- 
itive divisions  of  the  embryonic  brain,  but  are  either  the  result  of  a  transverse  sub- 
division, or  perhaps  of  an  offshoot  in  the  form  of  a  hernia  from  the  cerebral  lobes. 
Bearing  this  in  mind,  we  have  an  explanation  of  the  union  of  each  olfactory  with 
its  corresponding  cerebral  lobes  and  with  its  fellow,  in  Frogs,  which  is  simply  the 
result  of  incomplete  separation  or  of  arrested  development. 

II.  Cerebral  Lobes.  (Plate  I.  Figs.  1-9,  B.)  —  Agassiz,  in  examining  the  brains 
of  Fishes,  has  shown  that  those  of  the  same  natural  families  sometimes,  and  of  gen- 
era often,  affect  forms  which  to  a  certain  extent  are  characteristic,  and  something 
analogous  to  this  has  been  observed  by  Blanchard  to  exist  in  the  nervous  sys- 
tem of  Invertebrates.  A  comparison  of  the  cerebral  lobes  of  Siren,  Mcnopoma, 
Menobranchus,  Salamandra,  Triton,  and  Rana  (Plate  I.  Figs.  2,  4,  5),  will  show  that 
in  them  there  exist,  though  perhaps  not  strongly  marked,  certain  general  character- 
istic peculiarities,  which  consist  mainly  in  having  cerebral  lobes  with  an  elongated 
form,  with  sides  nearly  parallel  when  seen  from  above,  the  anterior  being  but  slightly 
more  narrow  than  the  posterior  extremity.  In  other  Reptiles,  the  cerebral  lobes 
have  a  more  triangular  form,  the  transverse  diameter  being  much  greater  behind 
than  in  front.  Measured  on  the  upper  surface,  each  cerebral  lobe  in  the  Bull-frog 
is  about  two  and  a  half  times  longer  than  broad,  and  the  breadth  of  the  two  lobes 
together  does  not  exceed  that  of  the  medulla  oblongata.  They  are  laterally  com- 
pressed, so  that  the  height  of  each  lobe  is  greater  than  its  breadth,  and  its  greatest 
elevation  is  at  .its  posterior  part.  (Plate  I.  Figs.  3  -  7.)  They  are  separated  by  a 
distinct  fissure,  which  may  be  seen  above  and  below,  and  which  presents  this  inter- 
esting feature,  that  it  extends  quite  through  from  the  upper  to  the  under  surface, 
being  closed  in  front,  however,  by  the  united  olfactory  lobes,  and  behind  by  the  meso- 
cerebrum ;  thus  presenting  the  opposite  state  of  things  to  that  which  exists  in 
Rays  and  some  Sharks,  where  the  two  are  so  completely  fused,  or,  perhaps  more 
correctly,  have  been  so  little  subdivided,  still  retaining  one  of  their  embryonic  fea- 
tures, as  to  have  the  appearance  of  a  single  lobe.  This  extended  separation  be- 
tween the  cerebral  lobes,  though  but  little  noticed,  certainly  exists  in  many  other 
Vertebrates.  Cuvier  speaks  of  it  in  Birds,  where  "  it  is  apparent  that  they  are  dis- 
tinct throughout  their  whole  height,  and  that  they  are  united  to  each  other  behind, 
near  the  anterior  commissure  of  the  brain."  *  Bojanus,  in  his  admirable  figures 
of  the  anatomy  of  Testudo  Europaa,  represents  a  similar  separation  between  the  cere- 
bral lobes,  though  it  is  not  referred  to  in  the  descriptions  of  the  plates.  His  Figs. 
88  and  89  show  the  two  hemispheres  disjoined  as  far  as  the  crura  cerebri.  Agassiz, 
in  the  Anatomie  des  Salmones,  Table  V.  Fig.  5,  has  represented  a  longitudinal 
section  of  the  brain  of  Salmo  fario,  in  which  it  appears  that  the  "  olfactory  lobes  " 
(cerebral  lobes,  cerebral  hemispheres  of  other  anatomists),  as  well  as  the  "  olfactory 
tubercles"  (olfactory  lobes  of  others),  are  likewise  wholly  separated  from  each 

•  Cuvier,  Le9ons  d'Anat.  Comp.,  3me  edit.,  Tom.  III.  p.  113. 


IV.  OF    RANA    PIPIENS.  9 

other.  This  complete  separation  of  these  lobes  in  the  animals  above  referred  to,  is 
certainly  an  interesting  anatomical  feature,  as  bearing  upon  the  physiology  of  the 
parts,  and  tending  to  prove  the  existence  of  complete  duality  of  function ;  for  it 
can  hardly  be  supposed  that  two  organs  so  completely  separated  could  be  any 
more  mutually  dependent  than  the  two  eyes  or  two  ears ;  each  is  the  seat  of  its 
own  functions  and  processes,  though  the  functions  of  the  two  sides  are  doubtless 
precisely  similar. 

The  closing  up  in  front  of  this  fissure  between  the  cerebral  lobes,  by  the  united 
olfactory  lobes,  leaves  an  opening  through  the  brain  from  above  downwards,  and 
this  might  at  first  sight  be  compared  to  the  ring  which  transmits  the  oesophagus  in 
the  Invertebrate  animals.  If  this  comparison  be  allowed,  it  would  afford  some  sup- 
port to  the  doctrine,  which  assumes  a  homology  between  the  nervous  centres  of  the 
Vertebrate  and  Articulate  divisions  of  the  animal  kingdom.  The  question  of  the 
correctness  of  such  a  comparison  will  necessarily  present  itself  in  the  course  of  the 
following  descriptions,  and  the  remarks  we  have  to  make  upon  it  may  be  not  im- 
properly presented  here. 

Although  frequent  attempts  have  been  made  to  homologize  the  nervous  systems 
of  Vertebrates  and  Articulates,  yet  in  reality  there  seems  to  exist  no  correct  basis 
on  which  the  alleged  homology  may  rest.  Among  the  earlier  advocates  of  this 
view  were  Gall  and  Spurzheim,  but  a  more  able  advocate  was  found  in  Geoffroy  St. 
Hilaire.  Still  more  recently,  the  doctrine  has  been  revived,  at  least  in  part.  In 
the  recent  edition  of  his  General  and  Comparative  Physiology,  Dr.  Carpenter  seems 
to  recognize  the  homology  of  certain  portions,  at  least,  of  the  nervous  systems  of 
Articulates  and  Vertebrates,  though  in  others  he  admits  simply  an,  analogy ;  after 
stating  that  there  is  nothing  in  the  Articulates  homologous  with  the  cerebrum  and 
cerebellum  of  the  Vertebrates,  he  says,  "  The  first  subcesophageal  ganglion,  which 
has  been  likened  to  the  latter  (the  cerebellum),  being  really  homologous,  as  the  dis- 
tribution of  its  nerves  abundantly  proves,  with  the  medulla  oblongata."  *  In  speak- 
ing of  the  spinal  chord,  he  says,  "  It  consists  of  a  continuous  tract  of  gray  matter 
inclosed  within  strands  of  longitudinal  fibres,  and  it  may  thus  be  regarded  as  anal- 
ogous to  the  ganglionic  chain  of  the  Articulates."  If  there  be  any  homology,  it 
seems  to  us  as  if  the  whole  nervous  system  of  the  Articulates,  as  far  as  it  is  devel- 
oped, should  be  homologous  with  a  corresponding  portion  of  that  of  the  Verte- 
brates. If  the  subcesophageal  ganglion  is  homologous  with  the  medulla  oblongata, 
that  which  follows  it  should  be  homologous  with  the  spinal  chord.  There  seems 
sufficient  ground  for  the  belief,  that  all  homology  between  the  nervous  systems  of 
the  two  divisions  is  as  much  contraindicated,  as  between  their  skeletons  or  their 
muscular  systems.  If  a  true  homology  existed,  we  ought  at  least  to  have  repre- 
sentatives from  the  Articulates  and  Vertebrates,  in  which  the  identity  would  be  ob- 
viously proximate,  if  not  absolute.  But  as  yet  there  has  been  described  no  instance 
where  the  spinal  chord,  structurally  considered,  is  fairly  and  distinctly  represented 
in  the  Articulates,  nor  among  Vertebrates  any  true  ganglionic  chain  with  an 

*  Gen.  and  Comp.  Phys.,  3d  edit.,  p.  1017. 


10  OX    THE   NERVOUS    SYSTEM  IV. 

• 

cesophageal  ring  through  which  the  oesophagus  passes.  The  existence  of  separate 
lateral  halves  of  the  spinal  chord  in  the  Vertebrate  embryo  has  been  adduced  as 
evidence  of  identity.  Has  there,  however,  ever  been  seen  an  embryo  of  a  Ver- 
tebrate in  which  there  were  developed  on  the  lateral  halves  of  the  spinal  chord 
itself,  distinct  and  separate  ganglionic  masses  united  with  the  masses  above  and 
below  them  by  nervous  fibres  only  1  It  is  true,  as  already  stated,  that  in  many  Ver- 
tebrates distinct  enlargements  of  the  chord  correspond  with  the  attachments  of  the 
different  pairs  of  spinal  nerves ;  but  still,  in  these  instances,  the  chord  never  loses 
its  vertebrate  type ;  there  is  always  at  least,  even  in  Amphioxus,  an  uninterrupted 
mass  of  cell  substance  occupying  the  entire  length  of  its  centre,  and  this  substance 
in  all  other  Vertebrates  is  inclosed  in  two  half-sheaths  of  longitudinal  nerve  tubes. 
The  likeness  recognized  between  the  suboesophageal  ganglion  and  medulla  oblon- 
gata  is  physiological,  but  not  anatomical ;  and  physiology,  all  philosophical  observers 
agree,  does  not  teach  us  homology.  The  wings  of  Birds  and  Insects,  physiologi- 
cally considered,  are  corresponding  parts ;  but  not  so  as  anatomical  structures.  On 
the  other  hand,  the  tongue  of  the  Giraffe,  of  the  Woodpecker,  the  Chameleon,  and 
the  Lamprey,  anatomically  considered,  are  identical  parts,  are  homologous  with  the 
organ  ordinarily  subservient  to  taste,  but,  physiologically  studied,  are  appropriated  to 
widely  different  uses.  Thus  the  suboesophageal  ganglion  may  be,  as  regards  its  func- 
tions, the  analogue  of  the  medulla  oblongata,  an  analogy,  however,  which  the  pure 
anatomist,  independently  of  experiment,  would  never  discover. 

Professor  Owen,  in  speaking  of  the  interspace  in  Fishes  "  produced  by  the  divarica- 
tion of  the  main  lateral  columns  of  the  encephalon,"  through  which  passes  the  mem- 
branous tube  (jnfundibulum)  connected  with  the  hypophysis,  asks,  "  Is  this  vertical 
slit  homologous  with  the  encephalic  ring  perforated  by  the  oesophagus  of  the  Inver- 
tebrata  ? "  *  The  homology  in  this  case  appears  to  be  opposed  by  the  fact,  that  the 
slit  in  question  in  the  Fish  opens  in  front  of  the  optic  lobes,  which  last,  if  there  be 
any  homology  between  the  nervous  systems  of  Vertebrates  and  Invertebrates,  would 
be  the  homologues  of  the  supracesophageal  ganglia  which  give  off  the  optic  nerves. 
The  slit  should  therefore  be  behind,  and  not  in  front  of  these  lobes. 

It  is  contended  that  the  homology  between  the  nervous  centres  of  Vertebrates 
and  Articulates  is  contraindicated  by  the  following  facts:  —  1st.  The  brain  and  spi- 
nal chord  are  enveloped  in  a  common  sheath,  the  vertebral  column  and  its  contained 
membranes,  and  are  never  in  the  same  cavity  with  the  viscera,  even  in  the  embryo ; 
while  the  ganglionic  chain  is  lodged  and  developed  in  the  common  cavity  with  the 
organs  of  organic  life.  2d.  In  Vertebrates  the  spinal  chord  is  always  on  the  back, 
and  the  ganglionic  chain  always  on  the  abdominal  side  in  the  Articulates.  3d.  One 
consists  of  a  continuous  mass  of  both  tubular  and  vesicular  structure,  while  in  the 
other  the  vesicular  structure  is  interrupted.  4th.  The  oesophageal  ring,  with  the 
oesophagus  inclosed,  never  exists  in  Vertebrates,  but  is  always  present  in  the 
Articulates,  in  common  with  nearly  all  other  Invertebrates.  5th.  The  embryonic 
conditions  of  the  two  systems  do  not  at  any  period  clearly  assimilate  each  other. 

*  Lectures  on  Comparative  Anatomy,  Vol.  II.,  Fishes,  p.  181. 


IV.  OF    RANA   PIPIENS.  11 

6th.  Two  parts,  to  be  homologous,  must  be  structurally  and  morphologically  similar, 
and  not  simply  the  seat  of  similar  processes. 

III.  Corpora  Striata.     (Plate  I.  Fig.  7,  C.)  —  The  parts  supposed  to  be  homolo- 
gous with  these  ganglia  are  but  very  imperfectly  developed,  and  present  themselves 
in  the  form  of  small  nodules  in  the  interior  of  the  cerebral  lobes,  and  will  be  again, 
referred  to  in  connection  with  the  ventricles  and  the  internal  configuration  of  the 
brain. 

IV.  Optic  Thalami.     (Plate  I.  Figs.  1-9,  D.) — Behind  the  cerebral  lobes  the 
encephalon  becomes  slightly  contracted,  and  its  breadth,  as  seen  from  above,  is 
formed  wholly  by  two  solid  bodies,  separated  from  each  other  by  a  distinct  fissure 
in  front,  but  behind  united  by  commissural  fibres.     (Fig.  6,  D.)     The  fissure  com- 
municates with  a  cavity  between  them.     Their  position  immediately  behind  the 
cerebral  lobes,  as  well  as  their  relation  to  the  part  next  to  be  described,  to  the  optic 
lobes  and  the  optic  nerves,  indicates  that  they  are  the  homologues  of  the  thalami 
optici  of  Mammals  and  Birds. 

V.  Pineal  Body.  .(Plate  I.  Figs.  2,  7,  9,  11,  12,  E.)  —  This  occupies  its  usual 
position  between  the  optic  thalami,  is  situated  at  their  anterior  extremity,  and  almost 
concealed  by  the  cerebral  lobes.     It  is  a  small  reddish  body,  the  presence  of  which 
is  not  easily  determined,  since  it  is  covered  with  a  loose  areolar  tissue,  which  unites 
it  to  the  investing  membranes,   and  consequently  is  usually  torn  oft'  in  removing 
them.     It  is  sustained  by  a  membranous  pedicle,  but  has  no  "  peduncles."     Its  mi- 
nute structure  is  quite  different  from  that  of  the  same  part  in  the  higher  Vertebrates, 
and  might  reasonably  lead  us  to  doubt  as  to  its  homology ;  in  truth,  independently 
of  its  position,  this  would  not  be  suspected.    Under  the  microscope  it  has  something 
of  the  form  of  a  mulberry,  and  is  highly  vascular.     Each  of  the  rounded  projec- 
tions on  its  surface  is  supplied  with  a  loop  of  a  bloodvessel,  all  the  loops  being 
derived  from  two  or  three  principal  trunks.    (Plate  I.  Figs.  11,  12.)    Externally  it  is 
invested  with  a  layer  of  ciliated  epithelium.     Within  the  epithelial  layer,  and  ap- 
parently among  the  bloodvessels,  are  scattered  rounded  cells  containing  granules, 
and  these  bear  a  close  resemblance  to  the  ganglion  cells  of  other  parts  of  the  brain. 
This  corresponds  with  the  description  of  the  same  part  in  Fishes,  as  given  by  Pro- 
fessor Owen.     It  is  in  them  a  constant  appendage  of  the  encephalon,  "  but  is  com- 
monly only  a  vasculo-membranous  pyramidal  sac  continued  from  the  third  ventricle. 
Some  medullary  matter  mingles  with  the  membranous  walls  in  Clupeoid  and  Cypri- 
noid  Fishes."  * 

The  existence  of  vibrating  cilia  on  the  surface,  and  of  vascular  loops  within,  are 
points  in  which  this  body  resembles  the  choroid  plexus  of  the  brains  of  Mammals 
as  described  by  Valentin ;  but  as  its  position  is  extra-ventricular,  we  have  no  author- 
ity for  identifying  it  with  that  organ.  The  cilia  on  its  surface  seem  to  indicate 
that  its  function,  in  part  at  least,  is  to  set  in  motion  the  fluids  secreted  by  itself  or 
some  of  the  adjoining  parts. f 

*  Owen,  op.  cit.,  Vol.  II.  p.  180. 

t  Comparative  Anatomy  of  the  Pineal  Body.  — It  exists,  according  to  Cuvier,  in  all  Fishes,  in  the  form 
of  a  small  globe  of  gray  matter,  very  distinct  in  the  common  Eel  and  the  Conger,  less  apparent  in  other 


12  ON    THE    NERVOUS    SYSTEM  IT. 

VL  Pituitary  Body.  (Hypophysis;  Plate  I.  Figs.  1,  3,  7,  8,  F.)  — This  organ 
is  as  universally  present  in  the  Vertebrate  series  as  the  preceding,  and  its  function 
is  equally  unknown.  In  Frogs  it  forms  a  very  distinct  portion  of  the  encephalon, 
is  situated  beneath  the  optic  lobes  at  a  short  distance  behind  the  optic  nerves,  and 
is  of  an  oval  form  with  its  greatest  diameter  in  a  transverse  direction  ;  it  has  a  short, 
hollow  membranous  infundibulum,  which  is  its  only  attachment  to  the  base  of  the 
brain,  and  is  consequently  easily  separated  by  very  slight  force,  when  the  orifice  com- 
municating with  the  ventricular  cavity  is  easily  seen.  A  body  which  has  received 
the  name  of  tuber  cinereum  is  found  between  it  and  the  decussation  of  the  optic 
nerves,  forms  a  slight  projection  from  the  under  surface  of  the  brain,  and  consti- 
tutes the  floor  of  the  third  ventricular  cavity ;  it  is  not,  however,  sufficiently  well 
defined  to  be  regarded  as  a  distinct  organ. 

VII.  Optic  Lobes.    (Plate  I.  Figs.  1,  2,  6,  7,  8,  G.)  —  In  consequence  of  their  form 
and  breadth,  the  optic  lobes  are  the  most  conspicuous  portions  of  the  brain,  and, 
after  the  cerebral  lobes,  the  largest.     They  consist  of  a  pair  of  oval  ganglia  flat- 
tened on  their  upper  surface,  their  longest  diameter  being  dijected  outwards  and 
forwards,  and  on  the  median  line,  where  the  two  come  in  contact  and  are  united,  they 
are  flattened,  as  it  were,  by  mutual  pressure.     When  seen  from  beneath  (Fig.  1, 
G),  they  make  a  prominent  projection  on  either  side  of  the  pituitary  body  and  the 
tuber  cinereum.     After  the  pia  mater  has  been  removed,  the  optic  tract  can  readily 
be  seen  in  its  passage  to  the  optic  thalami  and  optic  lobes.     (I'late  I.  Fig.  1.)* 

VIII.  Cerebellum.     (Plate  I.  Figs.  2,  3,  6,  7,  8,  H.)  —  Immediately  behind  and 
in  part  covered  by  the  optic  lobes,  is  the  cerebellum ;  which,  when  compared  with 
the  same  organ  in  the  higher  Vertebrates,  presents  a  more  striking  contrast  than 
do  either  of  the  other  cerebral  masses  with  their  respective  homologues.     In  Ba- 
trachians  generally,  the  cerebellum  does  not  seem  to  have  passed  beyond  the  mini- 
mum of  development  for  the  class  of  Reptiles,  an  inferiority  similar  to  that  met  with 
in  Petromyzon  and  Ammocoetes  among  Fishes.      It  consists  of  a  flattened  trans- 
verse band  of  cerebral  substance,  continuous  on  either  side  with  the  medulla  ob- 
longata;   its  posterior  border  is  slightly  elevated  (Figs.  7,  8,  H),  and  forms  the 

species,  and  is  inserted  between  the  "  hollow  lobes  "  (generally  regarded  as  the  optic  lobes)  and  the 
"  anterior  (or  cerebral)  lobes,"  by  two  small,  either  vascular  or  membranous  medullary  chords.  (Lefons, 
Tom.  III.  p.  135.)  In  the  Salmonidtz,  according  to  Agassiz,  the  pineal  body  consists  of  a  plexus  of  very 
slender  vessels  interwoven  and  anastomosing  with  each  other,  so  as  to  form  a  club-shaped  mass  attached  to 
a  slender  pedicle.  (Anat.  des  Salmones,  p.  132.)  According  to  Serres  (Anat.  Comp.  du  Cerveau,  Tom. 
II.  p.  483),  in  Squalus  squatina  "  it  surpasses  all  the  proportions  which  it  is  known  to  have  in  the  other 
classes."  He  also  states,  that  "  it  is  universally  present  in  Fishes,  but,  in  order  that  it  may  be  detected,  it 
must  be  examined  under  water."  In  Tortoises  it  is  much  more  distinct  than  in  Frogs,  is  easily  detected, 
but  having  apparently  the  same  vascular  structure  that  it  has  in  Batrachian  Reptiles.  Its  presence  in 
Mammals  and  Birds  is  beyond  a  doubt,  and  in  the  former  especially  consists  of  a  more  solid  mass,  having 
many  points  of  structural  resemblance  to  other  parts  of  the  encephalon.  The  calcareous  concretions 
which  Soemmering,  the  Wenzels,  Longet,  and  numerous  other  observers,  have  found  to  exist  so 
often,  perhaps  in  nearly  every  instance,  in  the  human  body,  are  seldom  or  not  at  all  found  in  the  other 
Vertebrates. 

*  For  pathological  facts  ahd  physiological  inferences  with  regard  to  the  optic  lobes,  see  the  description 
of  the  optic  nerves. 


IV.  OF    RANA   PIPIENS.  13 

anterior  limit  of  the  triangular  opening  of  the  fourth  ventricle,  and  beneath  it 
may  readily  be  seen  the  passage  from  the  fourth  to  the  third  ventricle.  Attached 
to  its  posterior  edge,  and  formed  by  the  folding  of  the  pia  mater,  is  a  vascular 
valve  or  plexus,  which  completely  covers  in  this  cavity.  According  to  R.  Wagner,* 
the  cerebellum  "  consists,  in  naked  Amphibia  and  Ophidia,  of  a  hollow  medullary 
layer."  In  the  dissections  of  Frogs  which  I  have  made,  I  have  in  no  instance 
been  able  to  verify  this  statement ;  for  it  has  always  presented  itself  in  the  form 
of  a  solid  body,  though  the  central  portion  is  more  transparent  than  the  cortical. 

The  low  degree  of  the  development  of  the  cerebellum  in  Frogs  naturally  suggests 
to  us  an  inquiry  as  to  the  nature  of  its  functions,  and  likewise  leads  to  the  con- 
clusion, that,  whatever  those  functions  are,  they  must,  on  analogical  grounds,  be 
supposed  to  have  a  low  state  of  activity  in  comparison  with  the  same  organ  in  those 
animals  in  which  it  is  proportionally  more  largely  developed.  The  low  develop- 
ment of  this  organ  in  Frogs  and  Cyclostome  Fishes  is  certainly  at  variance  with 
either  of  the  more  generally  received  theories  entertained  by  physiologists  of  the 
present  time ;  namely,  those  of  Gall  and  Spurzheim  on  the  one  hand,  and  of  Flou- 
rens  on  the  other.  It  would  be  difficult  to  reconcile  either  of  them,  or  perhaps  any 
existing  theory,  with  numerous  other  facts  afforded  by  comparative  anatomy,  all 
of  which  tend  to  show  a  vast  disproportion,  at  least,  between  the  size  of  the  cere- 
bellum and  the  activity  of  the  functions  of  which  it  is  alleged  to  be  the  seat. 
As  regards  the  theory  of  sexual  instinct,  this  function  is  certainly  not  less  strongly 
manifested  in  the  Lamprey  than  in  ordinary  Fishes,  as  the  Trout  or  the  Herring ; 
yet  how  widely  different  is  the  relative  size  of  the  organ  in  the  two !  Professor 
Owen  has  contrasted  Lampreys  with  the  Sharks,  showing  that  the  difference  in  the 
cerebellum  of  these  animals  is  entirely  disproportioned  to  any  known  distinction 
relating  to  the  sexual  instinct.f  The  well-known  experiments  of  Leuret,  though 
perhaps  less  extended  than  could  be  desired,  are,  as  far  as  they  go,  wholly  opposed 
to  the  hypothesis. 

Although  the  experiments  of  Flourens  and  his  followers  tend  to  show  a  con- 
nection between  locomotion  and  the  cerebellum,  disturbance  of  the  former  usually 
attending  injuries  inflicted  on  the  latter,  yet  his  theory  that  the  cerebellum  co- 
ordinates muscular  motions  is  opposed  by  numerous  anatomical  facts,  as  well  as  by 
some  of  the  results  of  pathology  ;  for  out  of  ninety-three  cases  of  lesions  of  the 
cerebellum,  Andral  found  but  one  to  sustain  the  theory  of  Flourens.  The  necessity 
for  coordinating  motions  in  Frogs,  animals  moving  with  four  legs,  is  as  great  as,  if 
not  greater  than,  in  most  Fishes,  moving  solely  by  the  aid  of  the  vertebral  column,  all 
their  principal  motions  being  produced  by  its  flexion  and  extension.  In  Petromyzon, 
with  its  still  more  rudimentary  cerebellum,  we  have  the  power  of  coordination  as 
great,  and  muscular  activity  as  intense,  during  the  breeding  season  at  least,  when  they 
stem  the  most  rapid  currents  and  ascend  falls  of  water,  as  in  the  Trout,  the  Sucker,  or 
the  Pike,  which  have  the  cerebellum  proportionally  much  longer.  We  will  take  one 

*  Elements  of  the  Comparative  Anatomy  of  the  Vertebrated  Animals,  p.  150. 
t  Lectures  on  Comp.  Anat.  and  Phys.  of  Vertebrated  Animals,  Part.  II.  p.  188. 


14  ON    THE    NERVOUS    SYSTEM  IV. 

more  illustration  of  the  inconsistency  of  this  theory  (and  it  equally  applies  to  that 
of  Gall  and  Spurzheim)  with  facts ;  we  will  contrast  the  organ  in  question,  as  it 
appeared  to  us  in  the  recent  dissection  of  a  Porpoise  (Delphinus  phoctena)  and  of  a 
Shark  (Carcharias  obscurus).  Both  of  these  animals  are  predaceous,  both  pursue 
their  prey  in  the  water,  both  are  endowed  with  great  rapidity  of  motion,  both  are 
capable  of  readily  and  suddenly  changing  their  direction,  and  both  move  by  the 
alternate  flexion  and  extension  of  the  vertebral  column ;  I  know  of  no  reason  for 
supposing  that  the  power  of  coordination  is  materially  different  in  the  two  ;  and  in 
these  instances  the  mass  of  the  body  was  in  the  two  nearly  the  same,  and  yet  the 
cerebellum  of  the  Porpoise  is  not  only  relatively,  but  absolutely,  several  times  larger 
than  the  whole  encephalon  of  any  known  Fish,  however  large. 

In  view  of  such  important  opposing  facts,  derived  from  comparative  anatomy  and 
pathology,  and  of  the  contradictory  results  of  experiments,  one  cannot  but  enter- 
tain a  doubt  that  the  problem  of  the  functions  of  the  cerebellum  is  yet  solved. 
The  suggestion  of  Dr.  Carpenter,  that  the  middle  lobe  may  be  the  seat  of  the 
sexual  instinct,  and  the  lateral  lobes  of  the  power  of  coordination,  loses  its  force 
when  it  is  remembered,  that  in  Fishes,  Reptiles,  and  Birds  even,  the  lateral  lobes 
either  do  not  exist,  or  are  in  a  rudimentary  condition,  entirely  disproportioned  to 
the  function  of  coordination.  If  the  size  of  the  organ  is  any  indication  of  its 
functional  activity,  the  cerebellum  is  not  proportional  to  the  amount  of  muscular 
fibre  set  in  motion,  nor  yet  to  the  combinations  of  motions  of  which  animals  are 
susceptible. 

SECTION  II.  —  INTERNAL  STRUCTURE  OF  THE  BRAIN. 

An  indication  of  imperfect  development  of  the  brain  in  animals  is  often  found  in 
the  existence  of  cavities  in  one  or  more  of  its  principal  masses.  An  immature  con- 
dition of  one  mass,  however,  by  no  means  involves  that  of  all  the  others.  In  some 
Sharks  the  nearly  solid  cerebral  lobes  accompany  a  hollow  cerebellum,  and  in 
other  Fishes  a  solid  cerebellum  and  cerebral  lobes,  as  in  the  Cod,  are  associated  with 
optic  lobes,  which  are  hollow.  In  Frogs,  with  the  exception  of  the  cerebellum  and 
optic  thalami,  all  the  principal  masses  are  hollow,  and  in  this  respect  manifest  but 
little  progress  beyond  an  embryonic  condition.  The  cavities  of  the  cerebral  and 
olfactory  lobes  communicate  freely  with  each  other,  though  there  is  no  communica- 
tion between  those  of  opposite  sides.  The  two  lobes  above  referred  to,  being  de- 
veloped from  the  same  vesicle,  do  not  manifest  any  separation  from  each  other  until 
some  time  after  the  tadpole  leaves  the  egg,  and  subsequently  the  distinction  between 
them  is  only  indicated  by  a  slight  constriction.  (Fig.  6.)  The  walls  of  the  cere- 
bral lobes  are  quite  thin  above  and  externally.  On  the  inner  wall  may  be  seen  in 
each  ventricle  two  projections ;  the  upper  and  longest  corresponding  with  an  external 
furrow,  and  which  may  therefore  be  regarded,  perhaps,  merely  as  a  convolution 
(Fig.  7);  and  the  lower  an  oval  ganglionic  body  (Fig.  7,  C),  in  which  may  be  seen 
terminating  some  of  the  white  fibres  prolonged  forwards  from  the  spinal  chord. 
This  body  is  solid,  and  its  position  in  the  ventricular  cavity,  its  connection  with 
the  white  fibres,  and  its  relation  to  the  optic  thalami,  which  are  directly  behind 


IV. 


OF    RANA    PIPIENS.  15 


it,  are  all  strong  indications  that  it  is  the  homologue  of  the  corpus  striatum.  Be- 
hind these  bodies  is  an  opening  which  communicates  with  the  third  ventricle  (Fig. 
8,  L),  and  above  this  another  directed  towards  and  above  the  optic  thalami, 
and  which  may  therefore  be  regarded  as  the  fissure  of  Bichat.  The  third  ven- 
tricle exists  in  the  form  of  a  fissure  between  the  optic  thalami  (Fig.  8,  M),  com- 
municating posteriorly  with  the  fourth  ventricle,  and  above  is  covered  over  pos- 
teriorly only  by  commissural  fibres.  The  optic  lobes  (Figs.  6,  7,  8,  D)  are  hollow, 
and  their  cavities  communicate  freely  with  each  other.  On  removing  their  upper 
walls  we  have  brought  into  view  two  masses,  which  are  seen  from  above  in  Fig.  6, 
and  in  section  in  Fig.  8,  which  nearly  fill  the  cavity,  allowing,  however,  a  passage 
beneath  and  between  them  to  the  fourth  ventricle. 

The  ventricles  of  both  cerebral  and  optic  lobes  are  lined  with  ciliated  epithelium, 
which  doubtless  serves  to  keep  in  motion  the  secreted  fluids  of  the  ventricular 
cavities,  a  function  in  all  probability  performed  by  the  cilia  of  the  choroid  plexus 
in  the  higher  Vertebrates.  Thus  we  have  suggested  to  us  again  the  old  hypothesis 
of  the  motion  of  the  fluids  contained  in  the  brain,  not  moved,  however,  by  the 
so-called  cerebral  pulsations,  but  by  an  agency  which,  when  the  theory  was  first 
propounded  on  a  purely  hypothetical  basis,  was  wholly  unknown. 

One  of  the  more  important  features  indicating  perfection  in  the  brain  of  the 
higher  animals  is  the  existence  of  commissures  between  its  different  segments  on 
opposite  sides.  The  corpus  collosum,  or  great  commissure  between  the  cerebral 
lobes,  does  not  appear  to  exist  in  or  below  the  Marsupials,  and  the  pons  Varolii  or 
cerebellar  commissure  is  confined  to  Mammals.  The  nearly  complete  separation  of 
the  cerebral  lobes  in  Frogs  would  seem  to  preclude  the  possibility  of  any  thing  like 
a  corpus  collosum  passing  from  the  one  lobe  to  the  other.  The  only  commissural 
fibres  which  I  have  been  able  to  trace  are  those  between  the  optic  thalami  (Fig. 
6,  D),  just  in  front  of  the  optic  lobes ;  also  between  the  same  parts  in  the  base  of 
the  brain. 

Although  great  labor  has  been  expended  in  attempting  to  unravel  the  micro- 
scopic structure  of  the  brain  in  Vertebrates,  as  yet  but  little  has  been  accomplished 
beyond  the  mere  demonstration  of  the  histological  elements  and  their  general  plan 
of  arrangement.  The  existence  of  tubular  fibres  and  of  vesicular  structure  is  ad- 
mitted in  the  nervous  system  of  both  Vertebrates  and  Invertebrates,  but  the  mode 
of  combination,  their  precise  anatomical  relationship,  is  still  unsettled ;  and  until 
that  relationship  can  be  determined,  but  little  progress  can  be  hoped  for  in  the 
explanation  of  the  mode  of  the  origin  and  transmission  of  nervous  force.  Its 
determination  is  no  less  important  to  the  physiology  of  the  nervous  system,  than 
the  discovery  of  the  circulation  of  the  blood  was  to  the  physiology  of  respiration 
or  nutrition.  Some  anatomists,  as  Hanover,  describe  the  vesicular  structure  as 
consisting  either  wholly  or  in  part  of  caudate  cells,  the  prolongations  of  which  are 
either  the  commencement  or  termination  of  nerve  tubes ;  this  view  has  also  been 
more  recently  maintained  by  Wagner  and  Robin.  Bidder  has  described  and  fig- 
ured nerve  tubes,  which  seem  to  dilate  into  ganglion  corpuscles  or  nerve  cells,  and 
then  revert  to  the  condition  of  nerve  tubes  beyond  the  cell,  so  that  the  cell,  accord- 


16  ON    TIIK    NEUVOUS    SYSTEM  IV. 

ing  to  this  view,  is  developed,  not  necessarily  at  the  beginning  or  end  of  a  tuhe, 
but  in  its  course.*  I  have  not  been,  able  to  detect  such  a  connection  in  any 
observations  which  I  have  made  on  the  brains  of  Frogs.  The  thin  walls  of  the 
cerebral  lobes  of  these  animals,  especially  when  young,  seemed  to  offer  a  favor- 
able opportunity  to  test  the  correctness  of  this  statement.  If  a  piece,  comprising 
the  whole  thickness  of  the  upper  part  of  the  lobes  above  mentioned,  be  placed 
under  the  microscope,  little  else  can  be  seen  than  the  vesicular  element,  though  the 
section  is  sufficiently  transparent  to  be  viewed  through  its  whole  thickness.  Here 
and  there  a  questionable  tube  may  be  found,  but  the  principal  structure,  besides 
the  cells,  is  that  of  the  capillary  vessels,  which  may  be  identified  by  their  containing 
blood  discs,  and  may  be  frequently  traced  dwindling  into  minute  empty  tubes, 
which  are  easily  mistaken  for  nerve  tubes.  If  a  piece  of  a  lobe  which  has  been 
macerated  in  alcohol  be  transferred  to  turpentine,  the  preparation  soon  becomes 
transparent,  when  its  minute  structure  can  be  determined.  In  the  cerebral  lobes 
of  Frogs  thus  treated,  spherical  cells  and  capillary  vessels  are  easily  detected,  but 
no  nerve  tubes.  The  longest  portion  of  the  whole  mass  obviously  consists  of  cells, 
and,  after  repeated  examinations  both  of  adults  and  embryos,  not  one  has  been 
found  presenting  the  caudate  condition.  Here,  then,  at  least,  we  have  an  instance 
in  which  the  cells  and  nerve  tubes  do  not  come  together,  —  in  which  they  are  not 
immediately  connected ;  and,  as  will  be  seen  in  the  spinal  chord,  continuity  is  not 
necessary  for  the  manifestation  of  nervous  force,  nor  is  contact  even.  In  other  parts, 
as  the  cerebellum,  optic  lobes,  optic  thalami,  the  tubes  and  cells  are  more  or  less 
intricately  combined,  the  first  forming  an  interlacement,  in  the  meshes  of  which  the 
cells  are  inclosed ;  but  even  here  no  continuity  between  the  twro  was  seen,  —  not  a 
single  instance  in  which  a  nerve  tube  arose  from  or  terminated  in  a  cell.  The  cells 
(Fig.  10,  Plate  I.)  are  quite  uniform  in  appearance,  from  whatever  part  of  the 
brain  they  may  be  derived.  The  only  variation  is  that  of  size.  The  cell  wall  is 
quite  thin,  and  so  easily  ruptured,  that  it  sustains  but  little  pressure,  and,  unless 
great  care  be  taken  to  protect  it,  it  will  be  found  quite  difficult  to  obtain  a  fair 
view  of  even  a  single  one.  Within,  the  cell  contains  numerous  minute  granules, 
which  fill  the  larger  portion  of  its  cavity,  leaving  a  thin  transparent  space  around 
the  circumference.  The  nerve  tubes,  whether  from  the  base  of  the  brain  or  from  the 
chord,  are  varicose  in  nearly  every  instance  ;  and  whether  this  condition  be  accidental 
or  not,  when  manipulated  with  the  greatest  care,  whether  viewed  with  or  without 
pressure,  even  when  perfectly  fresh  and  almost  living,  they  were  never  seen  in  any 
other  condition.  Every  attempt  to  determine  the  mode  of  termination  of  the  nerve 
tube  was  unsuccessful.  If,  however,  the  views  of  Wagner  and  some  of  the  more 
recent  writers  be  correct,  —  namely,  that,  before  the  nerves  terminate,  the  "  white 
substance  of  Schwann  "  disappears,  so  that  the  tube  contracts  and  becomes  invisible, 
except  with  the  highest  powers  of  the  microscope,  —  we  have  in  part  an  explanation 
of  the  difficulty.  Wagner  maintains  that  these  minute  tubes  are  lost  on  the  walls 

*  Zur  Lehre  von  dem  Verhaltniss  der  Ganglien-korper  zu  den  Nerven-fasern.     Neue  Beitrage  von 
Dr.  F.  H.  Bidder.     Nebst  einem  Anhange  von  Dr.  A.  W.  Volkman.     Leipzig.     1847. 


IV.  OF    RASA    PIPIENS.  17 

of  the  cells.  Such,  however,  cannot  be  the  case  in  the  cerebral  lobes,  since  there 
are  no  nerve  tubes  except  at  the  base  of  the  brain,  and  these  are  entirely  out  of 
proportion  to  the  cells  above  them. 

Having  failed  to  demonstrate  the  intimate  connection  between  the  tubes  and 
cells,  the  following  general  arrangement  of  the  two  was  nevertheless  easily  traced, 
and  the  more  easily  from  the  general  absence  of  commissural  fibres  in  the  en- 
cephalic masses.  The  appearance  which  first  of  all  attracts  the  eye  is  the  strong 
contrast  of  color  between  the  brain  and  the  spinal  chord,  the  first  seeming  almost 
gelatinous,  and  the  second  of  an  opaque  white,  a  contrast  depending  upon  the 
predominance  of  nerve  tubes  in  the  latter  and  of  nerve  cells  in  the  former.  The 
white  fibres  of  the  chord,  as  they  pass  forwards  from  the  medulla  oblongata,  may 
be  seen  entering  the  different  cerebral  masses,  as  indicated  in  the  plan.  (Fig.  9, 
Plate  I.)  Some  of  the  fibres  forming  the  edge  of  the  fourth  ventricle  can  be 
traced  into  the  cerebellum,  where  they  extend  towards  the  median  line ;  but  few  of 
them  reach  the  posterior  edge  of  this  organ,  which  has  the  gelatinous  appearance 
of  those  parts  which  consist  wholly  or  in  a  great  measure  of  cells.  Other  fibres 
from  the  lateral  portions  of  the  chord  are  traceable  to  the  optic  lobes,  on  entering 
which  they  are  crossed  by  the  fibres  of  the  optic  nerves,  coming  from  the  opposite 
direction  and  passing  them  externally.  The  remaining  portion  of  the  fibres  which 
are  continued  forwards  from  the  chord  pass  beneath  the  optic  lobes,  and  divide  into 
the  crura  cerebri,  where  they  can  be  more  easily  followed  by  slitting  the  brain  longi- 
tudinally ;  some  of  them  terminate  in  the  optic  thalami,  and  others,  quite  few  in 
number,  and  only  detected  by  the  microscope,  are  seen  to  enter  the  corpora  striata 
and  the  outer  walls  of  the  base  of  the  cerebral  lobes,  each  crus  subdividing  in  order 
to  reach  those  parts ;  finally,  the  last  traces  of  longitudinal  fibres  are  seen  follow- 
ing the  base  of  the  brain  as  far  forwards  as  the  olfactory  lobes.  No  portion  of  the 
brain  contains  so  many  nerve  tubes  as  the  optic  lobes  ;  they  are  derived  from  the 
two  sources  above  mentioned,  namely,  the  chord  and  the  optic  nerves,  and  within 
the  substance  of  the  lobes  the  two  kinds  are  so  completely  interwoven  and  inter- 
mixed, as  to  render  abortive  every  attempt  to  unravel  them,  and  determine  the  ex- 
istence of  a  definite  plan. 

The  general  result,  then,  which  has  been  obtained  from  an  examination  of  the 
minute  structure  of  the  brain,  is  simply  this:  —  1st.  That  each  of  the  cerebral 
masses  is  in  direct  connection  with  the  spinal  chord,  by  nerve  tubes  extending 
from  the  one  to  the  other.  2d.  All  the  longitudinal  fibres  of  the  brain  appear  to 
be  accounted  for,  in  the  species  here  described,  by  the  fibres  prolonged  from  the 
chord.  3d.  With  the  exception  of  the  optic  lobes,  the  cerebral  masses  consist 
mainly  of  cells,  none  of  which  are  caudate,  and  none  of  which  have  any  visible 
connection  with  the  nerve  tubes.  The  cells  are  all  nearly  spherical,  and  their 
contents  are  granular.  4th.  No  longitudinal  commissural  fibres  exist,  nor  any 
thing  analogous  to  a  fomix.  5th.  As  regards  the  functions  of  the  cerebral  lobes, 
their  bases  excepted,  whatever  force  they  originate,  whatever  impulses  they  trans- 
mit, and  whatever  impressions  they  receive,  all  must  be  effected  by  the  aid  of  cells 
alone ;  these  must  be  both  originators  and  conductors  of  nervous  force. 


18  ON    THE   NERVOUS    SYSTEM  IV. 


SECTION    III.  —  SPINAL  CHORD. 

As  is  almost  universally  the  case  in  the  Vertebrate  series,  this  portion  of  the  nervous 
system  consists  of  a  flattened  cylinder  terminating  posteriorly  in  a  conical  extremity, 
and  is  partially  divided  lengthwise  by  two  fissures,  one  on  the  upper  and  the  other 
on  the  under  surface ;  the  latter  in  Frogs  is  the  most  easily  traced,  and  when  the 
membranes  are  stripped  off,  the  right  and  left  halves  readily  separate  as  far  as  the 
gray  substance.  By  a  glance  at  Plate  I.  Fig.  1,  it  will  be  at  once  seen,  that  there 
exist  in  the  chord  three  enlargements  or  bulgings,  I,  L,  N,  at  nearly  equal  distances. 
The  first  of  these,  the  medulla  oblongata,  is  almost  universally  present  in  Vertebrate 
animals,  being  perhaps  really  deficient  in  Amphioxus  only;  but  the  second  and 
third  are  wanting  whenever  the  arms  and  legs  are  not  developed,  or  exist  in  a 
rudimentary  condition.  Among  Sauria  the  genus  Bipes  possesses  only  the  third 
or  crural,  and  Chirotes  only  the  second  or  brachial  enlargement ;  legs  only  being 
developed  in  the  first,  and  arms  in  the  second. 

When  seen  from  the  abdominal  or  lower  side,  as  in  Fig.  1,  these  three  enlarge- 
ments have  a  strong  resemblance  to  each  other,  and  it  is  at  once  suggested,  that 
they  are  serial  repetitions  of  similarly  constructed  parts.  In  addition  to  these,  I 
have  noticed  in  a  few  instances  a  slight  enlargement  of  the  chord  at  the  origin  of 
each  of  the  pairs  of  spinal  nerves,  and  from  observations  made  on  other  animals 
am  inclined  to  the  belief,  that  a  similar  condition  of  the  chord  exists  more 
generally  than  anatomists  have  been  disposed  to  admit,  and  that  there  is  con- 
sequently more  truth  in  the  disputed  statements  of  Gall  and  Spurzheim  with 
regard  to  this  point  of  anatomy  than  they  have  generally  received  credit  for. 
The  enlargements  in  question  are  quite  obvious  in  Menobranchus ;  also  in 
Lophius  Americanus,  as  stated  by  Cuvier,  though  the  correctness  of  this  last 
statement  has  been  called  in  question  by  Professor  Owen.  It  is  possible,  how- 
ever, that  in  the  European  species  it  may  not  exist;  in  the  American,  it  is  un- 
equivocally present. 

From  the  second  or  brachial  enlargement  is  given  off  a  large  trunk  distributed 
to  the  arms,  and  beyond  this  a  smaller  one,  which  sends  a  filament  to  the  preceding 
nerve  ;  the  contracted  portion  of  the  chord  which  follows  the  brachial  enlargement 
gives  off  the  nerves  to  the  walls  of  the  abdomen,  and  the  third  enlargement  sup- 
plies the  three  lumbar  nerves  and  the  minute  coccygeal  pair.  The  second  and 
third  bulgings  present  no  obvious  difference  as  regards  structure,  but  the  principal 
interest  which  attaches  to  them  is  the  proportion  between  their  size  and  the  limbs 
with  which  they  are  connected.  It  is  stated  by  Cuvier,  that  they  are  in  pro- 
portion to  the  "  force "  of  their  respective  limbs.  If  by  force  is  meant  the 
muscular  energy  and  development  of  the  limbs,  this  statement  does  not  appear 
to  be  sustained  in  the  present  instance,  nor  in  many  other  instances  brought 
to  notice  by  comparative  anatomy.  In  man  the  brachial  enlargement  is  always 
larger  than  the  crural,  though  the  legs  are  so  much  more  powerfully  developed 
than  the  arms,  and  the  same  is  true  of  the  greater  number  of  Mammals. 
In  Frogs  there  is  a  still  greater  disproportion  between  legs  and  arms,  yet 


IV. 


OF   RAMA   PIPIENS.  19 


there  is  not  a  corresponding  difference  in  the  size  of  the  bulgings.  They  cannot, 
therefore,  be  said  to  be  in  proportion  to  the  muscular  force  only  of  the  limbs, 
but  correspond  far  more  nearly  to  the  acuteness  of  the  sense  of  touch,  which  in 
Man  and  Mammals  is  more  delicate  in  the  hands  and  arms  than  in  the  legs  and  feet. 
In  Bats,  it  is  true  that  the  muscular  force  of  the  arms  is  greater  than  that  of  the 
legs,  and  that  the  brachial  far  surpasses  the  crural  enlargement ;  but,  at  the  same 
time,  the  sense  of  touch  in  the  membranes  of  the  wings  is  exalted  to  a  most  extra- 
ordinary degree.  In  Birds  the  posterior  bulging  is  almost  universally  the  largest, 
though  this  condition  is  in  part  dependent  upon  the  presence  of  the  rhomboidal 
sinus.  In  these  animals,  while  the  muscular  energy  of  the  wings  is  the  most  de- 
veloped, the  sensibility  of  the  feet  is  the  more  acute. 

A  transverse  section  of  the  chord,  when  viewed  with  a  low  magnifying  power, 
exhibits  the  external  or  white  substance  forming  two  crescentic  masses,  as  in 
Fig.  1,  a,  their  concavities  turned  towards  each  other  and  El&-  l- 

including  the  gray  substance,  b ;  this  last  seems  to  form 
the  only  bond  of  union  between  the  two  sides,  (and  in 
this  respect  agrees  with  the  results  of  Mr.  J.  L.  Clarke,* 
from  an  examination  of  the  chord  in  Man,)  the  white  col- 
umns being  quite  distinct  from  each  other,  and  having 
no  commissural  fibres  either  on  the  anterior  or  the  pos- 
terior face.  Under  the  microscope,  the  white  substance 
is  resolved  wholly  into  nerve  tubes,  and  in  the  gray  substance  even,  these  are  the 
most  conspicuous  element.  The  largest  portion  of  the  white  columns  consists  of 
longitudinal  nerve  tubes,  intermixed  with  others  which  are  transverse;  some  of 
these  last  are  continuous  with  the  roots  of  the  nerves,  and  can  be  seen  entering  the 
chord  passing  towards  the  centre,  and  between  the  longitudinal  fibres,  but  after 
entering  the  gray  substance  are  no  longer  traceable ;  as  shown  in  Fig.  14,  Plate 
L,  some  of  them  appear  to  join  the  longitudinal  series,  but  were  not  traced  far 
enough  to  determine  whether  they  did  not  ultimately  join  the  gray  substance  in 
their  immediate  neighborhood.! 

The  gray  substance,  besides  the  white  fibres  which  are  intermixed  with  it,  is  com- 
posed in  part  of  cells  more  or  less  spherical  or  polygonal,  such  as  are  met  with 
in  the  brain,  and,  in  addition,  of  distinct  caudate  cells,  such  as  are  represented  in 

*  Philosophical  Transactions,  1851. 

t  The  evidence  of  the  more  recent  microscopists  tends  to  show  that  nearly  all,  perhaps  all,  of  the 
nerve  roots  enter  the  gray  substance.  A  demonstration  of  this  fact,  with  regard  to  the  posterior  roots,  is 
easily  made  on  the  spinal  chord  of  a  fcetal  sheep,  where  they  have  the  peculiarity  of  passing  over  the 
outer  surface  of  the  posterior  columns  until  they  reach  the  median  line,  when  (still  on  the  exterior)  they 
descend  into  the  fissure  as  far  as  the  gray  substance,  in  which  they  are  wholly  lost.  Their  course  is 
easily  traced  with  a  low  doublet  or  even  the  naked  eye.  The  posterior  horn  of  gray  substance  reaches 
the  surface,  and  is  traceable  as  a  distinct  band  throughout  the  whole  length  of  the  chord.  In  the  in- 
stances which  the  writer  has  examined,  none  of  the  sensitive  roots  were  traced  into  the  posterior  white 
columns  ;  but  all  seemed  to  encircle  them,  and  enter  the  gray  substance  at  the  bottom  of  the  posterior 
fissure.  According  to  Mr.  Clarke,  the  posterior  roots  in  Man  are  traceable  through  the  posterior  columns 
into  the  gray  substance. 


20  ON    THE    NERVOUS    SYSTEM  IV. 

Fig.  «.  pig.  2.     It  is  not  easy,  however,  to  demonstrate  the  presence  of 

these  last  in  recent  specimens.  They  may  be  detected  readily, 
by  making  thin  sections  after  the  chord  has  been  hardened  in 
.  alcohol,  and  then  treating  them  in  the  manner  followed  by  Mr. 
Clarke.*  They  are  more  conspicuous  in  the  posterior  horns  of 
the  gray  substance,  where  they  form  a  well-defined  deposit, 
some  of  them  being  fusiform,  others  with  three  or  more  caudate  appendages.  After 
the  most  careful  examination,  I  have  not  detected  any  direct  connection  between 
these  caudate  appendages  and  nerve  tubes,  and  have  not  therefore  been  able  to  con- 
firm the  statement  of  Hanover  and  others,  that  nerve  tubes  originate  or  terminate  in 
nerve  cells.  The  deposit  of  caudate  cells  just  referred  to  seems  to  extend  through 
the  whole  length  of  the  posterior  horns  of  the  chord ;  they  were  not  detected  in  the 
anterior  horns. 

On  opening  the  chord  from  the  back  longitudinally,  two  white  tracts  or  columns 
are  traced  through  its  whole  length  and  continued  into  the  fourth  ventricle,  on  the 
floor  of  which  they  may  be  seen  without  dissection  ;  they  do  not,  however,  appear 
to  be  any  thing  else,  as  will  be  seen  hereafter,  than  the  lower  extremity  of  each 
lateral  crescent  of  white  substance,  as  seen  in  Fig.  1. 

In  the  sections  made  and  examined  according  to  Mr.  Clarke's  method,  I  have  al- 
ways found  a  canal  (Fig.  1,  c)  occupying  nearly  the  centre  of  the  chord;  it  is  lined 
by  a  well-defined  layer  of  oval  or  columnar  "epithelium  cells,  inclosing  a  distinct 
cavity,  which  in  all  probability  is  filled  with  serum.  This  canal  is  continuous  with 
the  cavity  of  the  fourth  ventricle.  BischofF,  Rokitansky,  and  others,  seem  to  regard 
the  canal  as  of  only  temporary  existence  in  the  human  body ;  but  Mr.  Clarke's 
observations  show  that  it  is  constant,  and  it  has  been  detached  in  many  adult 
animals ;  it  is  therefore  highly  probable  that  something  of  the  kind  exists  generally 
in  the  Vertebrate  division.  Consequently,  the  opinion  of  Gall  and  Spurzheim,  as 
to  the  existence  of  a  central  canal,  so  long  disputed,  is  fully  confirmed. 

As  already  stated,  the  medulla  oblongata,  when  seen  in  front  or  on  the  abdominal 
side,  appears  to  be  a  serial  repetition  of  the  crural  and  brachial  enlargements.  Ex- 
amined on  the  back,  the  resemblance  is  less  striking,  there  being  a  fourth  ventricle 
to  which  there  is  nothing  similar  in  the  other  portions.  If  it  has  been  more 
generally  described  in  connection  with  the  encephalon,  it  has  been  rather  from  its 
position  in  the  cranial  cavity,  than  from  any  marked  peculiarity  as  regards  structure, 
or  the  kind  of  function  of  which  it  is  the  seat.  When  morphologically  considered, 
it  is  reducible  to  the  common  type  of  the  chord,  and  the  more  complex  condition 
which  it  has  in  the  higher  animals,  in  consequence  of  the  existence  of  the  olives 
and  pyramids,  is  lost  in  the  descending  scale. 

The  fourth  ventricle  is  lined  with  a  thin  layer  of  gray  substance,  b  (Fig.  3),  and 
this  is  covered  by  a  layer  of  epithelium,  c.^  The  posterior  pyramids  (Plate  I.  Fig.  2,  L) 

*  This  consists  in  hardening  the  preparation  in  alcohol,  and  then  transferring  to  a  mixture  of  one  part 
of  acetic  acid  and  three  parts  of  alcohol,  in  which  it  is  left  for  one  or  two  hours ;  it  is  then  placed  for 
the  same  period  in  alcohol,  and  finally  transferred  to  turpentine,  which  expels  the  alcohol  and  leaves 
the  whole  transparent. 


IV. 


OF    RANA   PIPIENS.  21 


are  visible  on  each  side  of  the  fourth  ventricle,  and  two  pyramidal  tracts  are  con- 
tinued from  them  as  far  as  the  posterior  bulging  of  the  chord,  dilating  in  this  last 
as  well  as  in  the  brachial  enlargement ;  in  comparing  the  posterior  pyramids  with 
the  other  bulgings  of  the  pyramidal  tracts,  I  am  led  to  the  conclusion  that  they 
are  repetitions  of  similar  parts,  and  that  each  tract  enlarges  in  the  medulla  oblou- 
gata,  just  as  it  enlarges  in  the  brachial  or  crural  bulging. 

The  fourth  ventricle  results  from  the  separation,  or  perhaps  more  correctly  from 
the  want  of  union,  of  the  lateral  portions  of  the  chord  on  the  back.  By  a  comparison 
of  the  adjoining  Figs.  1  and  3,  it  will  fc  Fis-  3- 

be  seen  that  the  section  of  the  chord 
and  that  of  the  medulla  are  reducible  to 
the  same  typical  structure.  In  Fig.  3 
the  white  substance  is  still  presented  in 
the  form  of  two  crescents,  a,  but  their 
concavities,  instead  of  being  turned  towards  each  other,  are  directed  upwards,  and 
within  them  the  gray  substance,  b,  is  spread  out,  and  is  covered  by  an  epithelium 
layer,  c.  This  last  is  continuous  with,  and  is  an  expansion  of,  the  layer  of  epitlie- 
lium  which  lines  the  central  canal  of  the  chord,  and  the  gray  substance  is  likewise 
continuous  with  that  of  the  chord,  but  is  fissured  as  far  as  the  central  canal. 

Opposite  the  origins  of  the  vagus  and  trigeminus  nerves,  there  are  slight  gan- 
glionic  projections  into  the  cavity  of  the  ventricle;  but  they  are  very  indistinct, 
and  can  only  be  seen  after  close  examination. 

As  has  already  been  stated,  the  fourth  ventricle  is  closed  over  by  a  membranous 
covering,  which  in  its  minute  structure  is  reducible  to  a  vascular  plexus,  like  that 
of  the  pineal  body,  or  like  the  plexus  choroides  of  higher  animals  ;  the  vessels 
form  a  series  of  loops  connected  with  a  central  vessel,  and  projecting  to  the  right 
and  left ;  it  is  covered  with  ciliated  epithelium.  The  existence  of  vibrating  cilia 
on  the  ventricular  side,  and  of  a  fluid  in  the  cavity  of  the  ventricle,  involves 
the  necessity  of  the  fluid  being  kept  in  constant  motion.  From  what  has  been 
before  stated  with  regard  to  vibrating  cilia  in  the  cavity  of  the  ventricles  of 
the  brain  and  on  the  pituitary  body,  it  is  rendered  highly  probable  that  a  cir- 
culation of  serum  exists  through  the  cavities  of  the  ventricles,  passing  through  the 
passage  from  the  third  to  the  fourth  ventricle.  If  vibrating  cilia  should  hereafter 
be  detected  in  the  central  canal  of  the  spinal  chord,  this  last  would  also  be  the 
seat  of  a  similar  movement. 

The  change  of  form  which  the  spinal  chord  undergoes  during  the  progress  of 
development  is  one  of  its  most  interesting  features,  and  one  which  long  since  at- 
tracted attention.  The  phases  are  the  same  that  are  met  with  in  other  Vertebrates 
in  which  limbs  are  developed;  but  while  in  these  the  changes  take  place  with 
great  rapidity,  in  Frogs  generally  the  ichthyic  condition  of  the  chord  in  which 
there  are  no  enlargements  or  bulgings  continues  for  several  months,  the  eggs  being 
hatched  in  the  spring  and  the  complete  development  taking  place  in  the  latter  part 
of  the  summer.  In  Bull-frogs,  in  this  latitude  at  least  (42°  North),  development 
lasts  not  less  than  a  year,  as  the  tadpoles  hatched  in  the  spring  pass  the  following 
4 


22  OX    THE    NERVOUS    SYSTEM  IV. 

winter  in  the  same  condition,  the  metamorphosis  occurring  during  the  following 
spring  or  summer. 

Until  the  legs  begin  to  be  developed,  the  chord  presents  the  form  of  an  extremely 
elongated  cone,  and  the  bulgings,  as  was  noticed  by  Serres,  are  developed  simulta- 
neously with  the  legs.  I  have  not,  however,  been  able  to  confirm  the  statement 
made  by  him,  and  repeated  by  others,  that  the  caudal  portion  of  the  chord  is  short- 
ened as  the  legs  and  the  bulgings  are  developed.  According  to  my  observations, 
no  shortening  takes  place  until  the  absorption  of  the  tail  commences,  and  this 
happens  after  the  bulgings  are  formed  and  the  legs  have  acquired  their  growth. 
The  whole  of  the  caudal  prolongation,  however,  is  not  absorbed,  a  portion  being 
persistent,  and  eventually  becoming  enveloped  by  the  elongated  coccyx. 

The  caudal  portion  of  the  chord  in  the  tadpole  is  so  much  reduced  in  size,  that 
it  affords  an  unusually  good  opportunity  for  microscopic  examination.  It  is  much 
flattened,  has  no  fissures,  is  of  an  opaque  white  on  the  sides,  but  in  the  centre  a 
transparent  band  is  visible  through  its  whole  length.  Examined  with  a  power  of 
one  hundred  diameters,  or  even  less  (Plate  I.  Figs.  16,  17),  it  is  easily  resolved 
into  nerve  tubes  and  cells,  the  first  forming  the  opaque  lateral  bands,  and  the  latter 
a  transparent  central  stripe.  The  cells  ai'e  like  those  described  as  existing  in 
the  brain,  spheroidal,  filled  with  granules,  the  walls  attenuated  and  easily  rup- 
tured. Nona  of  them  are  caudate,  and  no  direct  connection  was  noticed  between 
nerve  tubes  and  cells,  the  former  being  almost  wholly  longitudinal,  running  with 
great  regularity  parallel  to  each  other,  and  giving  off  nerves  to  the  lateral  muscles 
which  form  so  large  a  portion  of  the  tail.  As  the  eye  traverses  the  chord  from  the 
apex  towards  the  brain,  there  will  be  seen,  as  we  approach  the  former,  here  and 
there  a  nerve  tube  running  more  or  less  obliquely  across  from  one  side  to  the 
other ;  a  little  farther  forwards  the  tubes  become  more  numerous,  until  at  length 
they  are  found  very  abundant  in  the  posterior  part  of  the  trunk.  Over  the  trans- 
parent central  portion  of  the  chord  there  may  be  seen,  with  a  very  high  power, 
very  minute  longitudinal  fibres  (Plate  I.  Figs.  15,  16),  which  appear  to  be  solid, 
and  have  not  the  double  outline  found  in  nerve  tubes  caused  by  the  substance 
of  Schwann. 

From  the  description  just  given,  it  will  be  seen  that  the  chord  gradually  becomes 
more  simple  in  the  caudal  portion,  that  transverse  fibres  gradually  become  less 
numerous,  and  are  eventually  omitted,  and  that  the  nerve  tubes  and  cells,  as  else- 
where, have  no  direct  connection.  The  lateral  strands  of  nerve  tubes  appear  to 
be  continuous  with  the  white  columns  of  the  chord  proper,  and  if  they  anywhere 
intermix  with  the  nerve  cells,  it  must  be  in  some  other  place  than  in  the  caudal 
portion. 

In  one  particular,  then,  the  caudal  prolongation  of  the  chord  in  the  tadpole 
differs  in  structure  from  that  of  the  true  chord,  in  having  the  nerve  roots  all 
ascending  towards  the  dorsal  region  of  the  chord,  and  none  of  them  passing 
among  the  cells  of  the  central  portion  opposite  to  the  points  at  which  they  are 
attached. 


IV.  OF    RAN  A    PIPIENS.  23 

SECTION  IV.  —  PERIPHERAL  PORTION  OF  THE  NERVOUS  SYSTEM. 

The  peripheral  system,  composed  of  the  different  nervous  trunks,  which  it  is  here 
proposed  to  describe  somewhat  in  detail,  is  in  Frogs  comparatively  simple  ;  far  more 
so  than  in  any  Mammals,  Birds,  or  higher  Reptiles,  and  more  so  even  than  in  most 
Fishes.  This  simplicity  results  in  part  from  the  reduction  in  number  both  of  cra- 
nial and  spinal  pairs  of  nerves  ;  in  the  former  it  seems  as  if  by  suppression  of  some 
of  them,  but  in  reality  it  is  by  the  union  of  two  or  more  pairs  which  in  other  ani- 
mals form  so  many  separate  nerves.  Another  condition  in  which  its  simplicity  is 
also  manifest  is  in  the  absence  of  those  extensive  anastomoses  and  plexuses,  which 
render  the  whole  system  of  the  animals  in  which  they  exist  so  intricate.  In  con- 
sequence of  these  peculiarities,  the  nervous  system  of  these  animals  becomes  a 
matter  very  interesting  to  the  physiologist  and  anatomist,  enabling  him  to  study 
the  whole  in  a  form  almost  typical,  perhaps  as  much  so  as  a  natural  form  ever 
is,  and  at  the  same  time  throwing  some  rays  of  light  on  the  subject  of  philo- 
sophical anatomy. 

The  number  of  pairs  of  nerves  connected  with  the  central  axis  and  escaping 
through  the  walls  of  the  cranium  or  the  vertebral  column,  does  not  exceed  in 
all  seventeen,  of  which  seven  are  given  off  either  by  the  cerebral  masses  or  the 
medulla  oblongata,*  and  ten  from  the  spinal  chord.  If  we  compare  the  number 
of  pairs  of  spinal  nerves,  as  indicated  by  the  number  of  vertebrae  in  the  different 
species  of  Vertebrates  noticed  in  the  tables  of  Cuvier,  it  will  be  found  that  in  none, 
a  few  Batrachians  alone  excepted,  is  it  reduced  so  low  as  in  Frogs.  According  to 
Cuvier  the  following  species  present  the  smallest  number  of  vertebra  in  the  classes 
to  which  they  respectively  belong. 

Gibbon  (Mammal),    ...........  31  Vertebrae. 

Hoopoe  (Bird), 35         " 

Chelys  anatomata  (Reptile), 38         " 

Ostracion  triangularis  (Fish),  .........  15         " 

Frogs  (Cuvier,  9  pairs), 10         " 

Pipa  (Surinam  Toad), 8         " 

With  regard  to  the  cranial  nerves,  there  exist  among  Fishes  even,  as  will  be 
seen  hereafter,  only  the  genera  Amphioxus,  Bdelostoma,  Myxine,  and  Lepidosiren 
in  which  the  number  is  known  to  be  actually  less,  the  first  having  but  three 
pairs,  Lepidosiren  five,  and  the  others  but  six.  Petromyzon,  according  to  Muller, 
has  nine  pairs,  and  according  to  Panizza,  eight.  In  the  larger  portion  of  the 
whole  Vertebrate  division,  at  least  ten  or  twelve  pairs  may  be  made  out,  the  ac- 
cessory nerve  being  the  one  which  is  most  frequently  deficient.  The  following 
table  exhibits  an  enumeration  of  the  cranial  nerves  of  Man  and  Mammals  con- 
trasted with  those  of  the  Frog,  showing  at  the  same  time  what  pairs  are  united 
in  the  latter,  so  as  to  reduce  the  whole  number  from  twelve  to  seven  pairs. 

*  "  In  the  brain  of  the  Frog  only  eight  separate  pairs  are  found,  the  facial,  glosso-pharyngeal,  acces- 
sory of  Willis,  and  hypoglossal  exhibiting  no  distinct  roots  "  ;  "  the  hypoglossal  is  given  off  by  the  first 
pair  of  cervical  nerves."  Wagner,  op.  cit,,  p.  151.  This  statement,  as  will  be  seen,  is  not  strictly  appli- 
cable to  the  present  species. 


4±  ON    THE    NERVOUS    STSTIM  IV. 

A.  Cranial  Nerves  :  — 

MAMMALS.  FKOG. 

I.  Olfactory I.  Olfactory. 

II.  Optic II.  Optic. 

III.  Motor  communis        ........  III.  Motor  communis. 

IV.  Patheticus IV.  Patheticus. 

V.  Trigeminus  \ 

VI.  Abducens     >  are  combined  and  form         ....  V.  Trigeminus. 

VII.  Facial  ) 

VIII.  Auditory VI.  Auditory. 

IX.  Glosso-pharyngeal  ) 

X.  Vagus  >  are  combined  and  form         .         .         .        VII.  Vagus. 

XI.  Accessory  ) 

XII.  Hypoglossal. 

B.  Spinal  Nerves  of  the  Frog.  I.     Hypoglossal. 

Brachial. 


II.) 
II-  1 


Abdominal. 

Crural. 
Coccygeal. 

From  this  table  it  will  be  seen  that  the  hypoglossal  nerve  in  the  Frog  occupies 
a  position  somewhat  anomalous,  forming  as  it  does  the  first  pair  of  the  spinal 
series.  If  this  were  added  to  the  cranial  nerves,  to  which  it  belongs  in  nearly 
all  other  Vertebrates,  the  whole  number  would  be  eight ;  namely,  three  special 
sense  nerves,  and  two  pairs  (viz.  the  motor  communis  and  patheticus)  endowed 
with  common  motor  properties,  and  three  (viz.  the  trigeminus,  vagus,  and  hypo- 
glossus)  having  both  motor  and  sensitive  filaments  combined.  To  these  'last  Sir 
Charles  Bell  applies  the  term  "  spinal,"  and  Muller  that  of  "  cranio-vertebral." 
A  larger  number  of  cranial  nerves  has  been  described -by  some  anatomists  in 
closely  allied  Batrachians,  but  after  repeated  dissections,  as  will  be  seen  in  the 
sequel,  there  seems  satisfactory  reason,  as  regards  the  species  here  under  consid- 
eration, for  adhering  to  the  enumeration  given  above. 

I.  Olfactory  Nerves.  (Plate  I.  Fig.  1,  i.  and  Plate  II.  Fig.  11,  B.)  — These  arise 
from  the  anterior  and  under  portion  of  the  olfactory  lobes,  their  union  with  which 
can  only  be  seen  distinctly  after  the  membranes  have  been  wholly  removed.  On 
the  anterior  extremity  of  the  lobe  they  form  a  kind  of  cap,  but  beneath  extend  in 
tfie  form  of  a  narrow  band,  situated  near  the  outer  edge,  as  far  as  the  union  of 
the  olfactory  with  the  cerebral  lobes,  where  they  terminate  in  a  rounded  bulb. 
From  this  band  extending  beneath  the  lobe,  there  is  given  off  at  its  commence- 
ment another  series  of  fibres,  which  are  directed  inwards,  separating  from  each 
other  and  forming  a  brush.  The  trunk  of  the  nerve  is  about  two  or  three  lines 
in  length,  is  directed  forwards,  and  each  nerve  escapes  through  a  separate  opening 
in  the  anomalous  bone,  described  by  Cuvier  as  the  " os  en  ceinture"  and  regarded 


IV.  OF    RAN  A    PIPIENS.  25 

by  him  as  the  representative  of  the  united  frontals  of  serpents,  and  by  others  as 
the  ethmoid.  The  nerve  trunks,  after  passing  these  openings,  divide  into  two 
branches,  each  of  which  breaks  up  into  a  brush  of  filaments,  and  are  distributed 
to  the  upper  and  under  surfaces  of  the  olfactory  pouches,  but  principally  to  the 
former. 

The  minute  structure  of  this  nerve,  as  in  other  animals,  is  quite  different  from 
that  of  the  other  sense  nerves.  Its  fibres  have  not  the  appearance  of  being  tubu- 
lar, are  not  varicose,  and  are  flattened  and  closely  matted  together,  resembling  the 
fibres  of  the  nerves  of  organic  life. 

II.  Optic  Nerves.  (Plate  I.  Figs.  1  and  3,  n.)  —  These,  when  stripped  of  their 
thick  sheath  exteriorly  to  the  cranium,  or  when  examined  within  the  cranial  cavity, 
are  a  little  less  voluminous  than  the  preceding  pair,  though  the  organ  of  sense  with 
which  they  are  connected  is  larger  and  more  complex.  Behind  the  decussation, 
each  nerve,  as  it  advances  towards  its  ganglionic  centre,  divides  into  two  distinct 
fasciculi  of  fibres  ;  the  anterior  fasciculus  is  directed  upwards,  its  fibres  being  dis- 
tributed to  the  anterior  portion  of  the  optic  lobe,  and  in  part  to  the  adjoining 
portion  of  the  optic  thalamus,  while  the  posterior,  passing  beneath  the  lobe,  enters 
it  upon  its  posterior  face.  If  the  brain  have  been  previously  macerated  in  strong 
alcohol,  this  demonstration  is  rendered  still  more  clear  by  cutting  through  the 
optic  nerves  at  the  decussation,  and  on  tracing  up  each  nerve  towards  its  origin, 
it  will  be  found  that  the  only  direction  in  which  the  fibres  may  be  separated 
without  rupture  is  towards  the  ganglionic  masses  above  mentioned.  The  connec- 
tion of  these  nerves  both  with  the  optic  lobes  and  optic  thalami  seems  unequivo- 
cal, and  is  a  fact  of  interest  bearing  on  the  connection  of  both  these  organs 
with  the  sense  of  vision,  and  this  view  is  supported  by  the  evidence  derived  from 
pathology  and  experiment.  Many  observers  have  shown,  by  dissection,  that  blind- 
ness of  long  standing  is  followed  by  atrophy  of  the  optic  lobes  (agreeably  to  the 
well-known  law  of  atrophy  following  disuse),  and  th'at  extensive  lesions  of  the 
lobes  are  attended  by  either  impairment  or  loss  of  vision.  In  recent  dissections 
of  Frogs,  similar  results  have  been  observed.  One  in  which  the  right  eye  had 
been  destroyed  had  atrophy  of  the  left  lobe,  which  was  reduced  by  nearly  one 
third  of  the  dimensions  of  that  of  the  opposite  side.  The  condition  of  the  nerve 
was  not  examined.  In  a  second  instance,  there  was  blindness  from  destruction 
of  the  left  eye,  in  which  there  was  atrophy  of  the  left  nerve  before  the  decussa- 
tion, of  the  right  nerve  behind  the  decussation,  and  of  the  right  optic  lobe.*  In 
neither  of  these  cases  was  there  any  marked  alteration  in  the  proportions  of  the 
optic  thalami. 

The  facts  furnished  by  comparative  anatomy,  however,  tend  to  show  that  vision 
is  not  the  sole  function  of  the  optic  lobes.  There  are  well-known  instances  of 
animals,  whose  lives  are  passed  either  in  caverns  or  localities  from  which  the  light 
is  excluded ;  one  of  the  most  remarkable  of  these  animals  is  the  Blind  Fish  (Am- 
llyopsis  spelceus,  Dekay)  from  the  Mammoth  Cave  of  Kentucky.  In  these  no 

*  American  Journal  of  Medical  Sciences,  edited  by  Isaac  Hayes,  M.  D.,  for  October,  1852. 


26  ON    THE    NERVODS    SYSTEM  IV. 

eyes  are  developed,*  and  yet  the  optic  lobes  do  not  remain  undeveloped  to  a  cor- 
responding degree,  but,  on  the  contrary,  acquire  a  proportional  size  nearly  equal 
to  that  of  other  Fishes  with  normal  vision.  While,  on  the  one  hand,  there  is  suffi- 
cient evidence  to  show  that  the  optic  lobes  are  connected  with  vision,  there  is,  on  the 
other,  evidence  to  prove  that  they  exist  without  vision,  or  entirely  out  of  proportion 
to  the  visual  organ,  as  in  Proteus. 

The  instances  of  Proteus  and  Amblyopsis  naturally  suggest  the  questions,  whether 
one  and  the  same  part  may  not  combine  functions  wholly  different  in  different 
animals,  and  whether  the  same  may  not  hold  true  with  regard  to  the  cerebral  or- 
gans which  is  known  to  obtain  with  regard  to  the  skeleton,  the  teeth,  the  tongue, 
and  the  nose,  that  identical  or  homologous  parts  in  different  animals  may  per- 
form functions  wholly  distinct.  If  the  doctrine  here  suggested  can  be  admitted 
(and  if  this  were  the  place  facts  could  be  cited  in  support  of  it),  may  we  not 
find  in  it  an  explanation  of  many  inconsistencies  which  now  exist  between  the  re- 
sults of  comparative  anatomy  and  physiology "? 

III.  Motor  Communis  (oculo-motor).  (Plate  I.  Fig.  1,  in.)  —  In  the  whole  Ver- 
tebrate series  of  animals,  there  is  generally  but  little  variety  in  this  nerve ;  but  the 
exceptional  cases  have  given  rise  to  some  difference  of  opinion  as  to  its  true  nature, 
and  as  to  its  relationship  to  the  trigeminus.  The  ordinary  distribution  of  this 
nerve  is  as  in  the  human  body.  On  entering  the  orbit,  it  divides  into  two  princi- 
pal branches ;  a  superior,  which  is  distributed  to  the  upper  rectus  and  levator  of  the 
upper  eyelid,  and  an  inferior,  distributed  to  the  rectus  internus,  and  the  rectus 
and  obliquus  inferior.  In  Batrachians  the  distribution  is  exceptional,  and  is  differ- 
ently described.  Cuvier  leaves  us  to  infer  that  it  is  the  same  as  in  Man.  Stannius 
describes  it  as  dividing  into  two  branches,  "  and  which  are  distributed  to  the  rectus 
superior  and  inferior,  and  obliquus  inferior ;  at  the  same  time,  in  Salamanders  and 
Tritons,  the  rectus  superior  receives  its  filaments  from  the  ophthalmic  nerve  "  (oph- 
thalmic branch  of  the  trigeminus). 

As  seen  in  my  dissections  the  motor  communis  arises  as  a  minute  filament  from 
the  under  surface  of  the  medulla  oblongata  near  the  median  line  at  its  anterior 
part  and  just  behind  the  pituitary  body ;  it  is  then  directed  outwards  and  forwards, 
perforates  a  little  obliquely  the  cartilaginous  sides  of  the  cranium,  just  in  front  of 
the  trigeminus ;  on  reaching  the  orbit,  it  crosses  the  ophthalmic  nerve  in  close 
contact,  and  has  the  appearance  of  becoming  incorporated  with  it,  which  has  led 
to  an  erroneous  description  on  the  part  of  some  anatomists.  The  nerves,  however, 
simply  cross,  there  being  no  intermixture  of  filaments  whatever.  The  branches 
given  off  by  the  motor  communis  are,  1st.  a  branch  passing  along  the  border 
of  the  rectus  internus  to  the  inferior  oblique ;  2d.  a  branch  to  the  rectus  internus ; 
3d.  to  the  rectus  inferior  ;  and,  4th.  to  the  rectus  superior.  (Plate  II.  Figs.  4, 5,  6.) 

*  Johannes  Muller  thinks  that  an  eye  actually  exists  ;  but  according  to  his  description,  it  is  "  an 
extremely  small  black  point,  without  a  cornea,  of  which  the  pigment  forms  the  external  layer,  and 
under  which  lies  a  colorless  membrane  ;  nothing  was  determined  on  with  certainty  with  regard  to  the 
contents  "  ;  no  optic  nerves  were  traced.  —  Memoir  on  the  Blind  Fishes  and  some  other  Animals  living  in 
the  Mammoth  Cave,  Ky.  By  Theodore  A.  Telkampf,  M.  D.  New  York  Journ.  Med.,  July,  1845. 


IV.  OF    RANA    PIPIENS.  27 

IV.  Patheticus.     (Plate  I.  Figs.  2  and  6,  iv.)  —  This  is  certainly  an  independent 
nerve,  and  at  its  origin  conforms  with  the  general  description  of  the  same  nerve  in 
other  animals.     It  arises  behind  the  optic  lobes,  from  the  part  corresponding  in 
position  with  the  valve  of  Vieussens  ;  it  perforates  very  obliquely  the  cartilaginous 
lateral  wall  of  the  cranium,  in  front  of  the  motor  communis ;  it  runs  parallel  to 
and  in  company  with  the  ophthalmic  nerve,  and  with  a  small  branch  of  this  last 
seems  to  form  an  anastomosis   (Plate  II.  Figs.  4,  5),  and  is  described  as  forming 
one  by  several  writers  ;  it  gives  no  branches,  however,  until  it  reaches  the  obliquus 
superior  muscle,  in  which  it  is  wholly  lost. 

Stannius  describes  this  nerve  as  "  distinct  in  the  Anourous  Batrachians,  and  as 
distributed  to  the  superior  oblique ;  but  in  Tritons  and  Salamanders  it  appears  to 
be  entirely  incorporated  with  the  trigeminus,  so  that  it  is  the  ophthalmic  branch 
which  furnishes  filaments  to  this  muscle."  *  Cuvier  doubts  the  existence  of  any 
communication  between  this  and  the  ophthalmic  nerve,  and  regards  the  supposed 
anastomosis  as  merely  an  apposition,  "  qu'il  ne  qu'accole  a  ce  nerf."  f  Vogt  has 
seen  a  filament  of  this  nerve  anastomose  with  the  ganglion  of  the  trigeminus  in 
Bufo  pantherius.  Fischer  could  not  detect  the  existence  of  the  patheticus  in  Sala- 
mandra  terrestris,  and  therefore  infers  that  it  is  derived  from  the  ophthalmic  branch 
of  the  fifth,  since  this  last  supplies  the  superior  oblique  with  its  motor  filaments. 

After  repeated  dissections,  I  am  satisfied  that  the  description  of  Cuvier  is  correct 
as  far  as  it  relates  to  Rana  pipiens,  and  that,  however  close  the  contact  be  between 
the  patheticus  and  the  branch  of  the  ophthalmic,  no  anastomosis  really  occurs ; 
and  am  led,  therefore,  to  the  conclusion,  that  the  patheticus,  which  in  Tritons  and 
Salamanders  is  a  branch  of  the  trigeminus,  is  in  Frogs  a  separate  and  independent 
nerve. 

V.  Trigeminus.     (Plate  I.  Fig.  1,  v.  ;  Plate  II.  Fig.  2,  v.)  — This  has  always  at- 
tracted the  attention  of  anatomists  and  physiologists,  on  account  of  its  extended  dis- 
tribution, its  connection  with  other  nerves,  and  its  relations  to  the  oi'gans  of  sense ; 
also  on  account  of  its  great  resemblance,  in  the  existence  of  a  ganglion,  to  a  common 
spinal  nerve.     In  Frogs  it  becomes  especially  interesting,  since,  in  addition  to  the 
three  principal  trunks  found  in  other  animals  (namely,  the  ophthalmic,  superior 
maxillary,  and  mandibular),  it  includes  the  facial  as  well  as  one  of  the  motor 
nerves  of  the  eye,  namely,  the  abducens.     The  different  roots  which  are  united  in 
the  trigeminus  are  widely  separated  from  each  other,  and,  as  here  described,  include 
all  the  roots  arising  from  the  medulla  oblongata,  and  which  become  connected  with 
the    trigeminal   ganglion.      The  principal  one,   and  which  corresponds  with   the 
trigeminus  proper,  arises  from  the  most  convex  part  of  the  lateral  portion  of  the 
medulla  oblongata,  by  several  distinct  fasciculi,  which  unite  and  form  a  single 
trunk,  that  is  directed  obliquely  forwards  and  enters  the  ganglion ;    this  trunk 
includes   both   motor   and   sensitive    filaments.      The  second  is   the   facial  (Plate 
I.   Fig.    1,  a),  which  emerges  from  the  medulla  in  close  contact  with  the  audi- 
tory nerve,  and,  after  accompanying  it  for  a  short  distance,  is  directed  obliquely 

*  Siebold  et  Stannius,  Nouveau  Manuel  d'Anatomie  Comparee,  Tom.  II.  p.  203. 
t  Lemons,  Tom.  HI.  p.  188. 


28  ON   THE   NERVOUS    SYSTEM  IV. 

forwards,  and  joins  the  principal  root  of  the  trigeminus,  into  the  ganglion  of  which 
it  enters.  The  third  (6)  root  is  equally  peculiar,  and  is  longer  and  far  more  slender 
than  either  of  the  others  ;  it  is  so  delicate,  that,  unless  great  caution  be  used,  it 
will  be  torn  away  in  the  removal  of  the  membranes.  The  facility  with  which  it 
is  destroyed  offers  a  probable  explanation  of  the  fact,  that  it  has  so  frequently 
escaped  observation.  Its  origin  is  about  midway  of  the  medulla  on  its  lower 
face,  and  quite  near  to  the  median  line ;  this  also  joins  the  principal  root,  and 
becomes  involved  in  the  Gasserian  ganglion.  The  origin  of  the  last-described 
root  corresponds  with  that  of  the  abducens,  of  which  there  can  be  no  doubt  that 
it  is  the  homologue,  as  shown  by  Vogt.* 

We  have  here,  then,  one  interesting  feature  of  the  trigeminus ;  namely,  that  all 
the  roots,  whether  motor  or  sensitive,  pass  through  the  ganglion,  a  condition  not 
usually  found  in  the  same  nerve  in  other  animals.  All  the  roots  thus  united  and 
connected  with  the  ganglion  escape  from  the  cranial  cavity  through  one  and  the 
same  foramen  in  the  (wing  of  the  ?)  sphenoid.  The  ganglion  is  usually  quite  near 
to  this  foramen,  may  even  occupy  it,  or  be  exterior  to  it.  The  Gasserian  ganglion 
in  its  shape  somewhat  resembles  the  same  part  in  the  human  body,  but  has  the 
characteristic  yellow  color  of  that  of  the  vagus  and  spinal  nerves.  From  its  convex 
surface,  three  large  trunks  and  one  smaller  one  are  given  off. 

A.  Ophthalmic  or  Orbitar  Branch.  (Plate  II.  Figs.  2,  3,  a.)  —  After  leaving  the 
ganglion  of  Gasser  this  nerve  is  directed  forwards  parallel  to  the  sides  of  the 
cranium,  till  it  reaches  the  co-ossified  frontals  or  the  "  os  en  ceinture  "  ;  this  it  per- 
forates, gains  its  cavity,  and  is  again  directed  forwards,  and  divides  into  two 
branches  ;  one  of  these,  the  superior,  crosses  the  olfactory  pouch  and  branches  of 
the  olfactory  nerve  above,  and,  inclining  towards  the  median  line,  is  distributed  to 
the  skin  on  the  lips  over  the  intermaxillary  region ;  the  other,  passing  externally  to 
the  olfactory  pouch,  is  lost  in  the  skin  behind  the  preceding.  The  upper  branch, 
crossing  the  olfactory  nerve  at  an  acute  angle,  gives  as  it  passes  small  branches  to 
the  pouch  itself.  (Plate  II.  Fig.  11.) 

Of  the  collateral  branches  of  this  nerve,  the  first  is  quite  small,  and  may  be 
traced  as  far  as  the  sclerotic,  which  it  perforates  near  the  optic  nerve,  while  other 
filaments  enter  it  nearer  to  the  cornea,  and  these  may  therefore  be  regarded  as  short 
and  long  ciliary  nerves.  The  next,  which  is  the  longest  of  the  collateral  branches, 
from  its  distribution  might  be  denominated  palatine  (Plate  II.  Fig.  2,  i),  though  not 
the  homologue  of  the  same  nerve  in  man,  since  this  last  is  derived  from  the  spheno- 
maxillary  ganglion,  which  is  a  dependence  of  the  maxillary  branch  of  the  trigemi- 
nus. The  palatine  nerve  in  Frogs  is  quite  easily  detected  on  raising  the  mucous 
membrane  of  the  roof  of  the  mouth,  to  which  it  gives  numerous  filaments,  and  is  di- 
rected parallel  and  runs  quite  near  to  the  median  line,  lying  just  beneath  the  base  of 

*  "  The  abducens  takes  its  origin  from  the  anterior  end  of  the  medulla  oblongata  near  the  median  line, 
runs  obliquely  forwards  towards  the  cavitas  occuli  under  the  fifth  nerve,  passes  near  the  ganglion  Gasseri, 
sending  a  branch  to  it,  while  the  greater  part  passes  beyond  this  ganglion  and  is  lost  in  the  muscles." 
C.  Vogt,  Beitrage  zur  Nevrologie  der  Reptllien.  Neuchatel,  1840.  See  Fischer,  Amphibiorum  Nu- 
dorum  Neurologies  Specimen,  p.  5. 


IV.  OF    HANA    PIPIEXS.  29 

the  skull.  A  little  in  front  of  the  globe  of  the  eye  it  divides  into  two  branches, 
one  of  which  extends  forwards  as  far  as  the  vomerine  bones  (c),  where  it  gives  fila- 
ments to  the  internal  nasal  orifice,  and  to  the  neighborhood  of  the  vomerine  teeth ; 
while  the  other,  the  larger,  bends  directly  outwards  (rf),  is  situated  behind  the 
palatine  bones,  till  it  reaches  the  inner  surface  of  the  upper  jaw,  where  it  forms  a 
distinct  union  with  the  superior  maxillary  nerve,  and  after  the  union  of  the  two 
their  terminal  branches  are  distributed  to  the  neighboring  mucous  surfaces.  The 
other  collateral  branches  of  the  ophthalmic  nerve  are  quite  minute,  one  of  which 
is  given  to  the  upper  eyelid  and  the  skin  in  front  of  it,  and  two  others  perforate 
the  united  frontals,  and  are  distributed  to  the  skin  over  the  nasal  cavities,  and  to 
that  of  the  nasal  orifices. 

B.  Upper  Maxillary  Branch.    (Plate  II.  Figs.  2  and  3,  e.) —  This  and  the  lower 
maxillary  branch  are  so  closely  connected  at  their  origin  from  the  ganglion,  that  for 
a  short  distance  they  appear  to  form  but  a  single  trunk,  though  with  a  little  care 
they  may  be  completely  separated.     They  become  disjoined  just  behind  the  globe 
of  the  eye,  where  the  upper  jaw  branch  gives  off  some  minute  filaments,  which 
pass  between  the  muscles  of  the  lower  jaw,  and  are  distributed  to  the  sensitive 
surface  of  the  eye.      A  small  branch  is  also  given  to  the  choanoid  muscle,  and 
it  is  near  this  point  that  the   abducens  leaves   the   trigeminus  to  reach  the  ex- 
ternal rectus  muscle.     The  terminal  filaments,  which  may  be  regarded  as  identical 
with  the  infra-orbitar  nerve  of  the  human  body,  are  lost  in  the  skin  beneath  and 
in  front  of  the  globe  of  the  eye.     A  collateral  branch  extends  inwards  beneath  the 
eye,  and  meets  with  the  palatine,  as  already  described,  at  d. 

C.  Mandibular  or  Lower  Jaw  Branch.      (Plate  II.  Figs.  2  and  3,  /.)  —  The  third 
principal  trunk  corresponds  in  its  distribution  with  the  same  nerve  in  the  higher 
animals.     Near  its  origin  branches  are  given  to  the  muscles  of  the  lower  jaw,  but 
on  reaching  the  angle  of  the  jaw  it  passes  over  it  to  the  outside;  then,  descending 
beneath,  it  runs  parallel  to  it  as  far  as  the  symphysis,  where  it  breaks  up  into  a 
brush.     Its  collateral  branches  are  distributed  to  the  skin  of  the  lower  jaw  and  to 
the  mylo-hyoid  muscle. 

D.  Facialis  (Portio  dura]."  (Plate  I.  Fig.  1,  a.)  —  The  nerve  in  Frogs  to  which 
this  name  has  been  given  is  quite  different,  in  its  mode  of  origin  and  of  distribution, 
from  that  to  which  the  name  has  been  given  in  the  higher  animals.     The  descrip- 
tions of  it  by  anatomists  are  far  from  coinciding  with  each  other,  and  will  be  found 
somewhat  at  variance  with  that  which  follows. 

In  describing  this  nerve,  Cuvier  does  not  appear  to  speak  from  personal  obser- 
vation when  he  says,  that  "  it  is  believed  that  a  branch  of  the  eighth  pair  (vagus)  in 
tailless  Batrachians,  as  it  goes  towards  the  trigeminus,  meets  with  a  branch  escaping 
from  the  semilunar  ganglion,  and  that  the  two  united  form  the  facial."  *  Wagner, 
in  speaking  of  the  cranial  nerves  in  Frogs,  says  that  the  facial  exhibits  no  distinct 
roots,  and  is  supplied  as  a  branch  of  the  acoustic.f  Muller,  referring  to  Volkman, 
remarks :  "  In  Frogs  Volkman  has  described  a  nerve  analogous  to  the  facial,  which 

*  Lemons  d'Anat.  Comp.,  2me  edit.,  Tom.  III.  p.  219. 

t  Elem.  Comp.  Anat.  Verteb.  Animals,  New  York,  1845,  p.  151. 

5 


30  ON*    THE   NERVOUS    SYST] ;M  IV. 

enters  the  ganglion  of  the  fifth  pair,  but  immediately  separates  again  from  it,  and 
is  continued  as  the  tympanic  branch  of  the  fifth,  till  it  joins  the  laryngeal  branch 
of  the  vagus.  This  laryngeal  branch  of  the  vagus  is  given  off  by  the  glosso- 
pharyngeal  branch  of  the  latter  nerve,  and  its  anastomosis  with  the  facial  may 
be  compared  to  the  similar  connection  of  the  glosso-pharyngcal  with  the  facial 
in  the  human  body."  *  Vogt,  in  his  excellent  memoir  on  the  nervous  system 
of  Reptiles,  describes  this  nerve  in  Toads,  after  leaving  the  ganglion,  as  "  winding 
around  the  labyrinth  to  the  cavitas  tympani,  behind  which  it  meets  with  a 
branch  of  the  glosso-pharyngeus  ;  these  two  united  nerves  bend  over  the  articu- 
lation of  the  lower  jaw,  and  branch  off  to  the  skin  and  muscles,  just  as  Volkman 
has  described  it."  f  Stannius  describes  the  nerve  somewhat  more  fully,  as  follows : 
"  Another  peculiarity  of  Fishes  is  found  in  this,  that  the  facial  nerve,  which  corre- 
sponds in  a  great  measure  with  the  opercular  branch  of  this  class,  sends  a  lower 
maxillaty  nerve,  which  accompanies  the  alveolar  branch  of  the  trigeminus  and 
anastomoses  with  it.  In  all  Anourous  Batrachians,  this  facial  or  jugular  nerve  re- 
ceives an  anastomosing  filament  from  the  first  branch  (analogous  to  the  glosso- 
pharyngeal)  of  the  vagus.  Its  first  branch  is  ordinarily  destined  to  the  skin  com- 
prised between  the  membrane  of  the  tympanum  and  the  angle  of  the  mouth 
(auricular  branch) ;  the  second  is  the  lower  alveolar  just  mentioned,  and  the  third 
is  distributed  in  part  to  the  sterno-hyoid,  and  in  part  to  the  skin  of  the  thoracic 
region."  t  The  following  may  be  added  to  the  quotation  made  above  from  Cuvier : 
"  In  tailless  Batrachians,  a  portion  of  the  facial  seems  to  be  furnished  by  the  fifth 
pair  under  the  form  of  a  fourth  branch  escaping  from  the  semilunar  ganglion."  & 
This,  however,  he  states  on  the  authority  of  Fischer. 

According  to  my  dissections,  the  following  appears  to  be  a  true  description  of 
the  origin,  connections,  and  ultimate  distribution  of  the  so-called  facial  nerve  in  the 
species  of  Frog  here  noticed.  The  manner  in  which  it  becomes  connected  with  the 
Gasserian  ganglion  has  already  been  noticed  (p.  27).  It  is  the  smallest  of  the  branches 
derived  from  the  ganglion,  which  it  leaves  at  its  inferior  angle,  and  is  directed  out- 
wards, passing  around  the  bony  walls  of  the  vestibule ;  it  passes  backwards  over  the 
columella,  with  which  it  is  in  close  contact,  and,  while  still  beneath  the  tympanic 
bony  circle,  is  joined  by  a  branch  from  the  glosso-pharyngeal  of  the  vagus,  or  by 
a  branch  from  a  common  trunk,  which  is  divided  into  the  glosso-pharyngeal  and 
this  anastomosing  branch.  (Plate  I.  Fig.  1,  c;  Plate  II.  Fig.  2,  g.)  The  single 
trunk  formed  by  the  union  of  these  two  branches  is  directed  downwards  and  back- 
wards behind  the  tympanic  cavity,  to  just  above  the  angle  of  the  jaw.  After  it  has 
reached  this  point,  it  is  far  from  easy  to  trace  its  terminal  branches,  but  after  many 
dissections,  both  with  and  without  water  acidulated  with  dilute  nitric  acid,  the  fol- 
lowing distribution  has  been  made  out,  and  it  goes  to  prove,  that,  although  the 
nerve  in  question  is  doubtless  the  homologue  of  the  facial  in  Man  and  Mammals, 

»  PhysioL,  Baly's  Trans.,  Vol.  I.  p.  834. 

t  Vogt,  Beitrage  zur  Nevrologie  der  Reptilien,  p.  52. 

J  Sicbold  et  Stannius,  Man.  d'Anat.  Comp.,  Paris,  1850,  Tom.  II.  p.  204. 

$  Cuvier,  Leyons,  Tom.  III.  p.  207. 


IV.  OF    RAN  A   PIPIENS.  31 

yet  its  distribution  and  properties  are  widely  different.  The  branches  from  the 
common  trunk  resulting  from  the  union  of  the  nerve  from  the  trigeminal  ganglion 
and  that  from  the  vagus  are  three,  liable,  however,  to  slight  variety,  sometimes  there 
being  but  two,  and  one  of  these  giving  off  the  third. 

a.  The  first  of  these  (Plate  II.  Fig.  2,  h)  is  directed  forwards  and  outwards,  and 
passes  over  the  tympanic  and  pterygoid  bones  just  above  the  articulation  of  the 
lower  jaw ;  it  gives  a  small  filament  to  the  walls  of  the  cavity  of  the  tympanum, 
after  passing  which  it  divides  into  two  terminal  branches,  one  of  which  is  distrib- 
uted to  the  skin  behind  the  angle  of  the  jaw,  and  to  the  sides  of  the  throat  in  the 
neighborhood  of  the  cicatrices  formed  by  the  obliteration  of  the  openings  through 
which  the  fore  legs  are  protruded  when  they  first  appear  externally ;  the  second  is 
directed  forwards,  and  is  lost  on  the  skin  covering  the  angle  and  the  posterior  half 
of  the  lower  jaw ;  near  its  termination  this  last  branch  forms  an  anastomosis  with 
the  external  lower  jaw  branch  of  the  trigeminus. 

b.  The  second  trunk  of  the  facial  (Plate  II.  Fig.  2,  i)  descends  along  the  horns 
of  the  os  hyoides,  but  in  its  passage  no  branches  were  detected  until  it  reached  the 
line  of  union  between  the  mylo-hyoid  muscle  and  the  skin  (which  occurs  on  either 
side,  midway  between  the  median  line  and  the  branch  of  the  lower  jaw) ;  there  it 
passes  to  and  is  distributed  in  the  skin  covering  the  throat  between  the  angles  of 
the  lower  jaw  under  the  larynx  and  in  front  of  the  sternum.     No  branches  what- 
ever were  traced  to  any  of  the  muscles  among  which  it  passed. 

c.  This  is  the  larger  of  the  three  (Plate  II.  Fig.  2,  k) ;  it  passes  inside  of  the 
angle  of  the  jaw,  reaches  the  inner  surface  of  this  last,  and  follows  the  line  of  union 
between  the  mylo-hyoid  and  lower  jaw  as  far  forwards  as  the  symphysis.     In  its 
course  it  gives  filaments  to  the  mucous  membrane  of  the  floor  of  the  mouth,  espe- 
cially at  the  posterior  part,  corresponding  with  the  position  of  the  air-sacs  of  the 
male  ;  the  largest  portion  of  its  terminal  filaments  reach  the  mucous  membrane  at 
the  union  of  this  last  with  the  jaw,  and  are  all  given  off  from  the  convex  side  of 
the  nerve ;  all  are  therefore  directed  outwards.     This  branch,  however,  is  not  in 
close  company  with  the  lower  jaw  branch  of  the  fifth,  as  stated  by  Stannixis,  though 
they  run  a  parallel  course. 

According  to  the  description  just  given  of  the  nerves  derived  from  the  trunk 
formed  by  the  union  of  branches  from  the  trigeminal  ganglion  and  the  vagus,  it 
must,  reasoning  from  analogy,  be  endowed  mainly,  if  not  wholly,  with  sensitive 
properties.  No  filaments  were  traced  to  muscles,  though  it  is  not  impossible  that 
some  minute  muscular  filaments  may  have  escaped  notice ;  if  any  do  exist,  they 
were  too  small  to  be  seen  with  a  lens  magnifying  three  diameters,  after  the  prepara- 
tion had  been  immersed  in  dilute  nitric  acid.  The  correctness  of  this  investigation 
by  anatomy  is  confirmed  by  the  evidence  derived  from  galvanism,  for  the  application 
of  this  agent  when  the  nerve  was  fairly  insulated  produced  no  muscular  contrac- 
tions ;  and  we  might  add  in  evidence  the  negative  fact,  that  the  muscles  of  mastica- 
tion and  those  of  the  hyoid  apparatus  are  respectively  supplied  from  the  lower  jaw 
branch  of  the  trigeminus  and  the  hypoglossus  nerves.  From  what  has  been  said, 
then,  it  follows  that  the  so-called  facial,  even  if  we  admit  the  existence  of  motor 


32  ON    THE    NERVOUS    SYSTEM  IV. 

properties,  is  quite  different  from  the  same  nerve  in  the  human  body ;  in  Man  it  is 
almost  wholly  motor,  having  no  sensitive  filaments,  except  such  as  are  derived  from 
anastomosis,  and  which  are  intended  to  give  a  muscle  its  ordinary  sensibility  ;  thus 
its  distribution  is  entirely  muscular.  In  Frogs,  on  the  contrary,  as  far  as  observed, 
its  distribution  is  wholly  cutaneous,  its  fibres  having  been  traced  to  the  skin  about 
the  tympanum,  the  angles  of  the  mouth,  the  submaxillary  and  lateral  jugular  region. 

The  description  given  above,  when  compared  with  those  of  others  which  precede 
it,  corresponds  with  that  of  Cuvier  and  of  Vogt  as  to  the  origin  of  its  vagal  and  tri- 
geminal  branches.  Cuvier  says  nothing  of  its  ultimate  distribution,  other  than 
would  lead  to  the  inference  that  it  has  the  ordinary  distribution  of  the  facialis. 
Vogt's  statement,  likewise  that  of  Volkman,  that  it  is  distributed  to  the  muscles  of 
the  lower  jaw,  I  have  not  been  able  to  verify.  There  does  not  appear  any  reason 
from  analogy,  or  from  the  dissections  just  described,  why  Volkman  should  apply  the 
term  laryngeal  to  the  anastomosing  branch  from  the  vagus.  An  anastomosis  exists 
between  the  facial  and  glosso-pharyngeal  nerves  in  the  human  body,  but  no  branch 
termed  laryngeal  is  given  off  from  them,  nor  is  the  nerve  in  question  entitled  to 
that  name  from  its  distribution.  The  only  true  laryngeal  nerve  in  Frogs,  as  will 
be  seen,  is  given  off,  not  by  the  nerve  just  referred  to,  but  by  the  third  or  visceral 
trunk  of  the  vagus,  and  is  the  homologue  of  the  recurrent  in  Man.  The  descrip- 
tion given  by  Stannius  is  certainly  the  most  complete,  and  he  is  almost  the  only  one 
who  seems  to  have  traced  the  branches  to  the  skin. 

The  anatomy  of  the  facialis  in  Salmofario,  as  given  by  Agassiz  after  his  original 
dissections,  shows  the  existence  in  this  Fish  of  a  condition  similar  to  that  of  Frogs. 
"  The  facial  nerve  escapes  from  the  brain  by  the  lateral  furrow  of  the  medulla  ob- 
longata ;  it  is  intimately  connected  with  the  root  of  the  acoustic,  and  is  separated 
from  the  trigeminus,  but  instead  of  following  the  course  of  the  acoustic,  its  fibres 
pass  obliquely  towards  the  ganglion  of  Gasser,  and,  uniting  to  its  inferior  face,  to 
the  fibres  of  the  trigeminus,  and  especially  to  the  suborbitar  branch  of  that  nerve. 
Although  there  is  evidently  a  mixture  of  these  two  nerves,  we  can  nevertheless  follow 
a  great  part  of  the  fibres  of  the  facial,  which  pass  directly  to  the  inferior  face  of 
the  ganglion,  into  a  single  nerve  which  escapes  from  the  cranium  through  the 
hole  in  the  great  wing  of  the  sphenoid  in  company  with  the  trigeminus."  *  While 
the  ultimate  distribution  is  different  in  the  two,  yet  Frogs  and  Trouts  have  this  in 
common,  that  the  facial  becomes  an  appendage  of  the  ganglion  of  Gasser,  and  as 
in  other  Fishes  it  becomes  more  or  less  blended  with  the  trigeminus.  As  it  is  in  no 
instance  bodily  combined  with  any  other  nerve,  we  may  safely  conclude  that,  phil- 
osophically considered,  the  facial  in  Man  is  a  dismemberment  of  the  trigeminus. 

VI.  Auditory.  (Plate  I.  Fig.  1,  vi.)  —  This  nerve  likewise  arises  from  the 
lateral  portion  of  the  medulla  oblongata  in  two  portions  closely  approximated  to 
each  other.  They  enter  the  vestibule,  sometimes  still  united  by  a  single  foramen, 
at  others  slightly  separated,  and  then  by  two  foramina.  I  have  noticed  one  of  these 
conditions  on  the  right  and  the  other  on  the  left  of  the  same  individual.  After 
entering  the  vestibule,  the  two  roots  separate  from  each  other,  and  are  distributed 

*  Agassiz  and  Vogt,  Anat.  des  Salmones,  p.  168  ;  also  Table  M,  Fig.  XVI. 


IV.  OF    RANA   PIPIENS.  33 

to  the  mass  of  calcareous  crystals  occupying  the  vestibular  cavity,  and  to  the  semi- 
circular canals. 

VII.  Vagus.  (Plate  I.  Fig.  1,  vn.;  Plate  II.  Fig.  2,  vn.)  —  This  is  the  last  of 
the  pairs  of  nerves  escaping  through  the  cranial  walls ;  it  arises  from  the  dorsal 
surface  of  the  medulla  oblongata  a  little  behind  its  lateral  portion,  by  three  or 
four  slightly  separated  roots.  The  most  posterior  of  these  is  attached  somewhat 
farther  towards  the  median  line  on  the  motor  or  lower  surface  than  the  others, 
and  may  therefore  be  compared  to  a  motor  root  of  a  common  spinal  nerve ;  if  this 
be  identical  with  any  separate  nerve  in  the  higher  animals,  it  is  with  the  acces- 
sory of  Willis,  though  it  has  not  that  peculiar  origin,  by  numerous  roots  extended 
for  some  distance  along  the  medulla,  as  in  higher  Reptiles ;  for  example,  in  the 
Tortoise.*  Reasons  for  believing  in  this  identity  will  be  found  in  the  description 
of  the  ultimate  distribution  of  the  nerve.  The  trunk  of  the  vagus  makes  its  exit 
from  the  cranial  cavity  through  a  hole  in  front  of  the  occipital  condyles,  which, 
when  examining  the  cranium  alone,  might  from  its  position  be  mistaken  for  the 
anterior  condyloid  foramen.  Immediately  after  leaving  the  cranial  cavity  it  be- 
comes involved  in  its  ganglion,  the  largest  of  the  whole  series  of  ganglia  connected 
with  the  cranio-vertebral  series  of  nerves.  All  the  root  fibres  probably  pass 
through  the  ganglion.  A  filament  of  the  sympathetic  nerve  unites  the  vagal  and 
hypoglossal  nerves  with  each  other,  and  between  the  two  is  a  ganglion,  the  first  of 
the  sympathetic  series.  The  vagal  trunks  are  three  in  number. 

A.  The  first  and  smallest  of  the  three  is  given  off  from  the  upper  portion  of  the 
ganglion  (Plate  I.  Fig.  1  and  Plate  II.  Fig.  2,  6),  is  directed  upwards  till  it  reaches 
the  skin  just  above  the  tympanum,  as  described  by  Volkman,  and  is  ultimately  dis- 
tributed to  the  integuments  between  the  tympanic  membranes  and  the  eyes,  and  on 
the  scapular  region  from  above  downwards  as  far  as  the  level  of  the  lower  edge  of 
the  tympanum.     This  nerve  is  supposed  b'y  Muller  to  be  the  remnant  of  the  ner- 
vus  lateralis  of  the  tadpoles,  a  view  which  does  not  seem  to  be  confirmed,  since  they 
have  the  nervus  lateralis  in  addition,  and  the  nerve  in  question  is  not  a  branch  of  the 
lateralis,  but  is  derived  directly  from  the  ganglion.     A  more  probable  supposition 
is  to  regai'd  it  as  representing  the  dorsal  branch  of  a  common  spinal  nerve,  a  branch 
which  is  repeated  for  every  pair  of  nerves  along  the  back ;  and  here  we  have  ad- 
ditional evidence  in  favor  of  the  identity  of  the  cranial  and  vertebral  series  of  nerves. 

B.  (Plate  I.  Fig.  1,#.)     This  trunk,  after  passing  outwards  one  or  two  lines,  di- 
vides into  two  branches,  one  of  which  is  directed  forwards,  and,  curving  around  the 
posterior  surface  of  the  vestibule,  joins  the  branch  from  the  trigeminus,  with  which 
it  forms  the  so-called  facial  nerve.      The  second  branch  is  directed  a  little  back- 
wards, descends  along  the  sides  of  the  neck,  where  a  minute  filament  is  given  to  the 
mucous  membrane  of  the  oesophagus,  passes  over  the  body  of  the  hyoid  bone,  giving 
filaments  to  the  mucous  membrane  of  the  floor  of  the  mouth,  then  along  the  upper 
surface  of  the  genio-hyoid  muscle  on  the  median  line  till  it  reaches  the  symphysis 
of  the  lower  jaw,  where  it  enters  the  base  of  the  tongue  and  is  distributed  to  the 
mucous  membrane  alone.     When  the  tongue  is  retracted,  this  nerve  is  thrown  into 

*  See  the  figures  of  Bojanus  in  his  Anatome  Test.  Europ.,  Plate  XXI.  Figs.  87  -  92. 


34  ON   THE    NERVOUS    SYSTEM 


IV. 


numerous  zigzag  folds,  which  adapt  it  to  the  peculiar  extensibility  of  that  organ. 
This  nerve  was  not  traced  to  any  of  the  muscles  among  which  it  passed,  nor  were 
any  contractions  of  the  hyoid  and  glossal  muscles  produced  when  the  nerve  was 
excited  by  galvanism,  proper  care  being  taken  to  secure  its  complete  insulation. 

The  distribution  of  this  nerve  to  the  mucous  membrane  of  the  tongue  pharynx 
indicates  that  it  is  a  nerve  of  sensation,  and  its  connection  with  the  vagus  shows 
that  it  can  be  no  other  than  the  glosso-pharyngeal,  which  in  the  higher  animals 
becomes  disjoined  and  forms  an  independent  pair. 

Muller  says :  "  The  glosso-pharyngeal  of  the  vagus  (in  Frogs)  is  the  only  branch 
analogous  to  the  glosso-pharyngeal  in  the  human  body,  and  this  he  regards  as  sup- 
plying the  place  of  the  gustatory  branch  of  the  fifth."  This  distribution  has  an  an- 
alogical interest,  since  if  it  be  the  seat  of  the  sense  of  taste  (and  it  is  the  only  sensi- 
tive nerve  going  to  the  tongue)  in  these  animals,  it  tends  to  show  that  the  glosso- 
pharyngeus  in  Man,  about  the  function  of  which  so  much  controversy  has  existed, 
may  be  a  gustatory  nerve.  "  The  glosso-pharyngeus  and  vagus  are  separate  at  their 
roots,  but  unite  immediately  in  the  skull  into  one  nerve  which  swells  into  a  large 
ganglion  outside  of  the  skull.  Before  the  glosso-pharyngeus  enters  the  vagus,  it 
sends  off  a  minute  branch,  which  runs  forwards  in  the  pia  mater  under  the  acousti- 
cus  over  the  cerebral  portion  of  the  sympatheticus,  and  penetrates  the  ganglion 
Gasseri.  According  to  Volkman's  description  it  does  not  exist  in  Rana,  neither 
could  I  convince  myself  with  certainty  of  its  existence  in  Bufo  cinereus,  for  the 
large  collection  in  the  membranes  of  the  brain  of  masses  consisting  of  micro- 
scopical crystals,  prevents  to  a  great  extent  the  preparation  of  so  fine  a  filament. 
In  Bufo  pantherinus,  however,  I  have  it  before  me  so  completely  prepared,  that  no 
doubt  can  remain  of  its  existence  and  its  course  as  described  above.  The  glosso- 
pharyngeus  leaves  the  ganglion  of  the  vagus  nearly  as  large  a  nerve  as  the  vagus 
itself,  gives  the  uniting  branch  to  the  facial  is  (which  Volkman  calls  the  laryngeal 
branch  of  the  vagus),  then  runs  downwards,  sends  a  branch  to  the  region  of  the 
glottis,  and  branches  in  the  tongue  as  far  as  the  tip.  The  real  vagus  runs  exactly 
the  course  described  by  Volkman,  along  the  oesophagus,  with  branches  to  the  im- 
mediate muscles,  and  gives  off  the  recurrent  and  the  branches  to  the  skin."  * 

C.  This  is  the  largest  of  the  vagal  branches,  and  corresponds  with  the  vagus  of 
the  higher  animals  (Plate  II.  Fig.  2,  /),  in  them  the  glosso-pharyngeal  being  a 
separate  nerve ;  it  descends  along  the  sides  of  the  neck,  having  the  glosso-pharyn- 
geal in  front  and  the  hypoglossal  behind,  the  latter  crossing  its  course  over  the 
stylo-hyoid  muscle.  The  first  branch  which  is  given  off  by  it  is  a  minute  twig 
to  the  stylo-hyoid  muscle  at  its  upper  part,  and  may  be  distinctly  traced  by 
the  naked  eye  among  its  fibres  as  far  as  the  middle.  A  little  below  this  a  much 
larger  brapch  leaves,  but  runs  parallel  to  its  course  for  a  short  distance,  but  soon 
passes  in  front  of  the  pulmonary  artery,  then  beneath,  and  ascends  a  short  dis- 
tance behind  it,  and  is  distributed  to  the  muscles  of  the  larynx,  f  This,  therefore, 

*  Vogt,  op,  cit. 

t  Weber  has  shown  that  even  in  the  Frog  a  branch  of  the  vagus  gives  off  a  filament  which  takes  a 
retrograde  course  to  the  larynx.  Muller's  Physiol.,  Baly's  Trans.,  2d  edit.,  Vol.  I.  p.  838. 


IV.  OF    EANA   PIPIENS.  35 

must  be  regarded  as  the  homologue  of  the  "  inferior  laryngeal "  or  "  recurrent " 
nerve  of  the  human  anatomist.  That  this  homology  is  correct  is  still  further 
indicated  by  the  influence  of  galvanism,  which,  when  applied  high  up  on  the  sides 
of  the  neck,  causes  contraction  of  the  laryngeal  muscles.  No  superior  laryngeal 
was  detected.  A  little  lower  down  than  the  origin  of  the  recurrent  branch,  the 
whole  trunk  divides  into  two  fasciculi  of  nervous  fibres,  one  of  which  forms  the 
cesophageal  plexus,  and  the  other  is  readily  traced  to  the  heart  and  lungs. 

From  the  preceding  description,  it  appears  that  the  vagus  arises  from  the  lateral 
portion  of  the  medulla  oblongata,  the  only  distinction  between  its  root  fibres  being 
the  slight  separation  of  the  anterior  ones  from  the  rest,  which  arise  nearer  the 
median  line  on  the  motor  side  of  the  chord.  All  its  fibres  appear  to  enter  the  gan- 
glion ;  its  branches  are,  —  1.  to  the  skin  behind  the  tympanum  and  over  the  scap- 
ula ;  2.  an  anastomosing  branch  to  one  from  the  trigeminus  forming  the  "  facial " ; 
3.  the  glosso-pharyngeal ;  4.  the  splanchnic  portion,  distributed  to  the  heart,  lungs, 
oesophagus,  and  stomach.  Of  the  terminal  filaments  of  its  different  trunks,  some 
are  distributed  to  the  skin,  others  to  mucous  membranes,  as  to  the  oesophagus, 
tongue,  and  probably  to  the  respiratory  passages  ;  there  are  also  motor  filaments  to 
the  stylo-hyoid,  to  the  larynx,  and  to  the  spinal  muscles  immediately  above  its  gan- 
glion ;  these  muscles  it  causes  to  contract  when  stimulated  by  galvanism. 

The  vagus  nerve  has  been  quite  differently  described  by  different  anatomists,  and 
it  is  only  required  that  their  descriptions  should  be  placed  side  by  side  to  render 
evident  their  occasional  inconsistency.  Cuvier,  whose  accuracy  is  generally  so  ad- 
mirable, in  describing  this  nerve  seems  to  speak  from  analogy  rather  than  personal 
observation.  He  speaks  of  its  "  accessory  branch  "  as  if  it  were  a  distinct  trunk, 
when  he  says,  "  The  accessory  is  found  in  all  orders  of  Reptiles,  and  is  arranged  as 
in  Birds."  *  He  further  states,  "  From  the  ganglion  of  the  vagus  in  Frogs  is  given 
off  a  nerve  for  the  muscles  of  the  jaws,  and  another  for  the  tongue  "  ;  the  latter 
has  just  been  shown  to  exist,  but  I  have  never  traced  any  branches  to  the  muscles 
of  the  jaws,  nor  have  these  muscles  contracted  when  the  vagus  has  been  stimulated 
by  galvanism.  Opposed  to  this  statement  is  the  fact  that  the  trigeminal  branches 
are  distributed  to  the  muscles  of  mastication,  and  that  they  contract  when  the  tri- 
geminus is  galvanized. 

Wagner,  in  speaking  of  the  vagus,  says :  "  Some  very  delicate  nervous  radicles, 
arising  from  the  inferior  tracts  of  the  medulla  oblongata  near  to  its  anterior  fissure, 
unite  with  it  and  appear  to  correspond  with  the  glosso-pharyngeal."  J-  This  glosso- 
pharyngeal  is  one  of  the  principal  trunks  from  the  ganglion,  and  cannot  be  iden- 
tified with  either  of  the  bundles  of  roots  ;  it  has  been  shown  to  be  a  sensitive  and 
not  a  motor  nerve,  as  it  would  be  were  Wagner's  description  correct,  which  makes 
it  arise  near  the  anterior  fissure. 

Longet  states,  that  "  in  Frogs  there  is  given  off  from  the  ganglion  of  the  vagus 
a  branch  which  is  distributed  to  the  muscles  of  the  jaws."  J  This  is  a  repetition 
of  the  statement  of  Cuvier. 

*  Legons  d'Anat.  Comp.,  Tom.  III.  p.  226.  J  Syst.  Nerveuse,  Tom.  II.  p.  371. 

t  Comp.  Anat.  of  Verteb.  Animals,  p.  151,  Am.  ed. 


36  ON    THE    NERVOUS    SYSTEM  IT. 

Vogt  describes  the  glosso-pharyngeal  as  giving  a  branch  to  the  facial,  "  after 
which  it  runs  downwards,  sends  a  branch  to  the  region  of  the  glottis,  and  branches 
to  the  tongue  as  far  as  the  tip  " ;  the  branch  to  the  glottis  I  have  not  seen ;  and 
as  he  describes  in  addition  a  "  recurrent  branch,"  he  evidently  does  not  refer  to 
this  last 

Wagner  leaves  us  to  infer  that  he  finds  a  part  of  the  accessory  nerve  of  the 
vagus,  when  he  says,  "  Some  of  the  roots  of  the  accessory  nerve  appear  to  be 
absent." 

Muller,  quoting  Weber,  says :  "  In  Frogs  a  branch  from  .the  ganglion  of  the 
vagus  goes  to  the  muscles  of  the  lower  jaw.  It  is  the  jugular  branch  of  Volkman, 
who  has  shown  its  motor  influence  to  be  derived  from  a  branch  of  the  facial  nerve 
which  has  coalesced  with  it.  It  is  distributed  partly  to  the  hyoid  muscles  and 
partly  to  the  muscles  of  the  lower  jaw."  *  I  have  seen  no  other  nerve  to  which 
this  description  is  applicable,  than  that  formed  by  the  union  of  a  branch  from  the 
vagus  and  the  trigeminus  ;  the  latter  branch,  arising  from  the  side  of  the  acoustic 
nerve,  joins  the  ganglion  of  the  trigeminus,  and  afterward  the  branch  from  the 
vagus.  According  to  my  dissections,  none  of  its  branches  are  muscular;  although 
they  pass  among  the  muscles  of  the  jaw,  they  were  not  traced  to  them,  nor  do  they 
cause  them  to  contract  when  galvanized ;  a  small  filament  is  given  off  behind  the 
tympanum,  which  I  at  first  thought  was  distributed  to  the  masseter,  but  afterwards 
felt  satisfied  that  I  could  trace  it  wholly  to  the  membranous  walls  of  the  tympanic 
cavity.  Volkman's  statement,  that  it  is  distributed  partly  to  the  hyoid  muscles,  is 
also  rendered  improbable  by  the  positive  demonstration  that  these  muscles  get  their 
nervous  filaments  from  the  hypoglossus. 

Nervus  Lateralis.  (Plate  II.  Fig.  9.)  —  There  exists  in  Fishes,  as  has  long 
been  familiarly  known  to  comparative  anatomists,  a  peculiar  nerve,  usually  a  branch 
of  the  vagus,  though  it  may  sometimes  be  the  result  of  the  union  of  branches 
from  the  vagus  and  trigeminus ;  or  it  may  be  derived  from  the  trigeminus  alone, 
which,  from  extending  along  the  side  of  the  body  beneath  the  lateral  line,  has 
received  the  name  of  lateral  nerve.  "  In  Salmo,  Clupea,  and  Acipenser  it  is  formed 
exclusively  by  the  vagus,  but  in  many  Fishes,  as  Belone,  Coitus,  Cyprinus,  it  is 
formed  by  a  branch  of  the  vagus  which  receives  branches  from  the  trigeminus."  j" 
In  addition  to  this,  there  exists  a  nerve,  first  described  by  Weber,  called  the 
dorsal  nerve,  formed  generally  by  a  union  of  filaments  from  the  fifth  and  vagus, 
which,  escaping  by  an  especial  opening  in  the  parietal  and  interparietal  bones, 
extends  along  the  whole  length  of  the  dorsal  fin,  receiving  filaments  from  the  inter- 
costals,  and  giving  nerves  to  the  muscles  of  the  fin  rays.  In  Silurus  it  is  derived 
from  the  fifth  only,  and  in  some  others  from  the  vagus.J  The  use  of  either  of  these 
nerves  is  unknown ;  Muller  failed  to  produce  muscular  contractions  by  irritating 
with  galvanism  the  lateral  nerve  of  the  carp.  It  is  then  in  all  probability  simply 
a  sensitive  nerve. 

*  Physiol.,  Vol.  I.  p.  838. 

t  Owen,  Lects.  on  Comp.  Anat,  Vol.  II.  p.  196. 

J  See  Cuvier,  LeQons  d'Anat.  Comp.,  Tom.  HI.  p.  212. 


IV.  OF    RANA   PIPIENS.  37 

It  is  an  interesting  feature  in  the  anatomy  of  Batrachian  Reptiles,  which  in  so 
many  respects  resemble  Fishes,  that  they  should  have,  some  of  them  temporarily 
and  others  permanently,  a  nerve  which  is  strictly  analogous  to  the  nervus  lateralis 
of  Fishes.  It  has  been  found  by  Van  Deen  to  exist  in  Proteus,  by  Meyer  in 
Menopoma,  and  by  Kuhn  in  Tritons,  and  probably  it  exists  in  all  the  other  Urodels. 
Among  the  Anourous  Batrachians  it  was  first  noticed  in  Frogs,  by  Van  Deen. 

Its  distribution,  as  it  was  presented  in  the  tadpoles  of  R.  pipiens,  is  as  follows. 
(Plate  II.  Fig.  9.)  The  vagus  escapes  through  the  cartilaginous  occiput  as  a  single 
trunk,  and  from  its  ganglion  are  given  off  the  following  branches  :  —  1st.  A  branch 
which  unites  with  another  from  the  trigeminus,  and  forms  the  facial.  2d.  A  cutane- 
ous nerve,  distributed  to  the  skin  of  the  neck  and  that  of  the  branchial  region. 
3d  and  4th.  Two  delicate  filaments,  which,  one  of  them  dividing,  furnish  three 
nerves  (d),  one  to  each  of  the  branchial  arches.  5th.  The  nervus  lateralis  (c)  ;  at  its 
origin,  this,  like  the  preceding  nerves,  is  concealed  by  the  spinal  muscles  attached  to 
the  occiput ;  having  extended  outwards  as  far  as  the  skin,  it  passes  along  the  side 
of  the  abdomen  just  beneath  the  edge  of  the  spinal  muscles,  and  is  continued  along 
the  side  of  the  tail  in  the  groove  formed  by  the  union  of  the  upper  and  lower 
series  of  caudal  muscular  bands.  Soon  after  leaving  the  vagal  ganglion,  the 
nervus  lateralis  gives  off  a  delicate  filament  («,  6),  which  does  not  appear  to  have 
been  noticed  hitherto,  and  which  is  easily  traced,  if  the  parts  have  been  macerated 
in  dilute  nitric  acid ;  this  branch  ascends  and  is  directed  backwards  till  it  reaches 
the  base  of  the  fold  of  skin  forming  the  upper  portion  of  the  caudal  fin,  along  the 
base  of  which  it  extends  towards  its  termination. 

While  no  doubt  exists  as  to  the  identity  of  the  nervus  lateralis,  there  can  be 
little  that  the  branch  just  described  is  identical  with  the  nervus  dorsalis  of  Weber, 
it  being,  as  in  some  Fishes,  a  branch  of  the  vagus  ;  in  the  case  of  Frogs  it  is  wholly 
cutaneous,  there  being  no  muscles  connected  with  the  skin,  and  in  Fishes  it  seems 
questionable  whether  this  nerve  is  motor  or  sensitive.  In  Cuvier's  Comparative 
Anatomy  the  following  remark  occurs  in  connection  with  the  vagus,  which  it  is  of 
interest  to  mention  here :  "  Up  to  the  present  time,  no  nerve  analogous  to  the 
dorsal  has  been  found  in  Reptiles.  Nevertheless,  the  parietal  bones  of  Saurians 
are  pierced  with  a  foramen  like  those  of  Fishes."  * 

•The  observation  of  the  existence  of  a  dorsal  nerve  gives  additional  importance  to 
the  discovery  of  the  nervus  lateralis  by  Van  Deen ;  and  if  to  these  we  add  those 
branches  of  the  vagus  described  above,  which  pass  along  the  branchial  arches,  the 
analogy  of  the  larvae  of  Batrachians  to  Fishes  becomes  much  more  striking  than 
there  has  been  reason  hitherto  to  regard  it. 

SECTION  V.  —  PHILOSOPHICAL  ANATOMY  OF  THE  CRANIAL  NERVES  AND  SKULL. 

In  the  table  at  the  commencement  of  Section  IV.,  the  cranial  nerves  of  Man 
and  Mammals,  and  those  of  the  Frog,  are  contrasted ;  it  is  there  shown  what  nerves 
in  the  two  correspond,  and  how  it  is  that,  by  the  union  of  two  or  more  nerves,  the 

*  Lemons  d'Anat.  Comp.,  Tom.  III.  p.  229. 

6 


38 


OX    THE    NERVOUS    SYSTEM 


IV. 


twelve  pairs  in  the  one  case  are  reduced  to  seven  in  the  other.  In  the  subjoined 
tabular  view  of  the  cranial  nerves,  as  they  are  presented  in  some  of  the  different 
members  of  the  Vertebrate  series,  it  is  further  seen  that  there  exists  a  transition 
from  the  more  simple  condition,  in  AmpkiOMU,  ^fycinc,  and  Lepidosiren  among 
Fishes,  and  in  Frogs  among  Reptiles,  where  the  nerves  are  less  numerous,  to  the 
most  complex,  in  Mammals  and  Man  ;  that  the  trigeminus  and  vagus,  as  we 
traverse  the  series,  are,  as  it  were,  split  up  and  dismembered,  so  as  to  make  from 
the  smaller  number  in  the  one  case  the  larger  in  the  other. 

Table  of  the  Number  of  Pairs  of  Cranial  Nerves  found  in  some  of  ike  Members  of  the  Four  Classes 

of  Vertebrates. 


oir. 

Op. 

M.  c. 

Palh. 

Trig. 

Abd. 

Fac. 

Aud. 

Gl.  p. 

Vagus 

Access 

Hyp. 

Tolal. 

Man  (Soemmering), 

I. 

II. 

III. 

IV. 

V. 

VI. 

VII 

VIII.    IX. 

Y 

XI. 

XII. 

12 

Testudo  Europaea  (Bojanus), 

I. 

II. 

III. 

IV. 

V. 

VI. 

VII. 

VIII. 

IX. 

X. 

XI.    XII. 

12 

Goose  (Swan), 

I. 

II. 

III. 

IV. 

V. 

VI. 

VII. 

VIII. 

IX. 

X. 

? 

XII. 

11 

Boa  (Swan), 

I. 

II. 

III. 

IV. 

V. 

? 

VII. 

VIII. 

IX. 

X. 

XII. 

10 

Salmo  (Agassiz), 

I. 

II. 

III. 

IV. 

V. 

VI. 

VII. 

VIII. 

IX. 

X. 

XII. 

11 

Raia  (Swan), 

I. 

II. 

III. 

IV. 

V. 

VI. 

VIII. 

IX. 

X. 

XII.    10 

Bufo  palmarum  (Fischer), 

I. 

II. 

III. 

IV. 

V. 

VI. 

VIII. 

X. 

XI. 

XII. 

10 

Petromyzon  (J.  Muller), 

I. 

II. 

III. 

IV. 

V. 

VII 

VIII. 

X. 

XII. 

9 

"           (Panizza), 

I. 

II. 

III. 

V. 

VII. 

VIII. 

X. 

XII. 

8 

Gadus  morrhua  (Swan), 

I. 

II. 

III. 

IV. 

V. 

VI. 

VIII. 

X. 

XII. 

9 

Rana  pipiens  (J.  W.), 

I. 

II. 

III. 

IV. 

V. 

VIII. 

X. 

7 

Bdellostoma  (Muller), 

I. 

II. 

V. 

VII. 

VIII. 

X. 

6 

Myxine  (Muller), 

I. 

II. 

V. 

VII. 

VIII. 

X. 

6 

Lepidosiren  (Owen), 

I. 

11. 

V. 

VIII. 

X. 

5 

Amphioxus,* 

I. 

II. 

V. 

3 

The  instances  in  which  the  nerves  are  reduced  to  the  lowest  degree  of  numerical 
simplicity  are  very  few,  in  comparison  with  those  in  which  the  larger  portion,  if 
not  the  whole  series,  of  twelve  exists.  This  simplicity  is  not,  however,  regulated  by 
the  zoological  position  of  the  animal ;  for  in  Frogs  there  exist  but  seven  pairs  of 
cranial  nerves,  whilst  in  most  Fishes  eleven  are  found,  —  the  whole  series,  in  fact, 


*  This  enumeration  of  the  nerves  of  Amphioxus  deviates  from  that  of  Quatrefages,  in  his  admirable 
memoir  on  the  anatomy  of  this  interesting  Vertebrate.  By  reference  to  the  figures  of  Quatrefages,  it 
will  be  seen  that  the  five  pairs  described  by  him  may  be  easily  reduced  to  three,  if  we  regard  the  branches 
I  and  m  (Plate  XI.)  as  forming  but  one  nerve,  and  corresponding  to  the  ascending  and  descending 
branches  of  a  common  spinal  nerve  in  the  same  animal,  and  the  branches  o  and  p  (Figs.  4  and  5)  as 
accessory  filaments  to  the  nerve  /.  The  branch  m  does  not  vary  materially  in  its  size  and  distribution 
from  the  corresponding  part  in  the  pairs  which  precede.it.  The  great  size  of  the  branch  /  is  at  once  ex- 
plained when  compared  with  the  greater  amount  of  surface  which  it  supplies,  and  the  more  acute  sensi- 
bility which  exists  about  the  head.  The  branches  Z,  m,  o,  p,  would  therefore  form  but  a  single  nerve, 
which  may  be  compared  with  the  trigeminus  ;  and  if  to  this  we  add  the  optic  and  olfactory,  we  have  two 
pairs  of  special  sense  nerves  and  one  of  cranio-spinal  nerves.  Rathke  regards  all  the  nerves  as  true 
spinal  ones,  and  the  brain  as  wholly  deficient.  See  Quatrefages,  Annales  des  Sci.  Nat.,  p.  197. 
Oct.,  1845. 


IV.  OF   RANA    PIPIENS.  39 

which  is  met  with  in  Man,  except  the  spinal  accessory.  It  does  not  appear,  that 
in  one  and  the  same  animal  the  number  of  cranial  nerves  is  reduced  so  low 
as  six  pairs,  except  in  the  lowest  of  Fishes,  namely,  in  the  genera  Amphioxus, 
Myxine,  Lepidosiren,  and  Bdellostoma.* 

While  the  cranial  nerves  of  Frogs  are  less  simple  than  in  the  genera  just  men- 
tioned, they  are  more  so  than  in  any  Mammals,  Birds,  or  Beptiles,  except  the  allied 
Batrachians ;  and  they  are  especially  interesting  as  showing  the  greatest  reduction 
met  with  in  any  air-breathing  Vertebrates.  By  tracing  out  the  distribution  of  some 
of  the  branches  of  the  trigeminus  and  vagus,  we  are  enabled  to  identify  them  with 
the  separate  pairs  of  nerves  into  which  they  are  resolved  in  the  ascending  series. 
The  branch  from  the  vagus  distributed  to  the  tongue  is  easily  identified  with 
the  glosso-pharyngeal,  and  the  branch  to  the  muscles  of  the  shoulder  with  the 
spinal  accessory ;  thus  we  have  a  demonstration  of  the  fact,  that  the  vagus  is  made 
up  by  the  union  of  three  nerves,  which  in  Man  are  so  many  independent  pairs. 
In  like  manner,  some  of  the  branches  of  the  trigeminus  are  identified  with  separate 
pairs  of  nerves  in  the  higher  Vertebrates,  as,  for  example,  the  facial,  and  the  motor 
externus;  in  Salamanders,  the  patheticus,  and  some  (as  the  rectus  superior,  pp. 
26,  27),  if  not  all,  of  the  branches  of  the  motor  communis.  Thus  the  theory  which 
makes  the  typical  number  of  cranial  nerves  (independently  of  the  special  sense 
nerves)  three  pairs,  namely,  trigeminus,  vagus,  and  hypoglossus,  becomes  highly 
probable. 

As  regards  the  special  sense  nerves,  they  have  some  peculiarities  which  seem  to 
indicate  that  they  are  of  a  different  order  from  all  the  rest  of  the  nerves  connected 
with  the  cerebro-spinal  axis.  Their  peculiarities  relate,  —  1st,  to  the  fact  that 
they  are  connected  with  special  organs  of  sense ;  2d,  to  their  development. 

According  to  the  ablest  embryologists  of  the  present  day,  common  spinal  nerves, 
and  the  same  is  true  of  the  cranio-spinal  nerves,  do  not  shoot  out  from  the 'respec- 
tive portions  of  the  chord  to  which  they  are  attached,  but  are  developed  in  the 
tissues  where  they  are  respectively  found,  and  this  independently  of  the  central 
axis,  just  as  the  bloodvessels  of  the  germinating  membrane  are  developed  inde- 
pendently of  the  central  organ  of  circulation.  This  view,  or  something  very  near 
it,  was  maintained  by  Gall,  and  more  recently  has  been  presented  by  Bischoff, 
Kolliker,  and  others. 

Such  is  not  the  mode  of  the  development  of  the  special  sense  nerves.  According 
to  Reichert  and  the  more  recent  observers,  the  special  sense  nerves,  as  well  as  a  por- 
tion of  the  organ  of  sense  itself,  are  the  result,  in  the  first  instance,  of  a  kind  of 
hernia,  or  protrusion  of  a  portion  of  the  embryonic  cerebral  vesicles,  which  are 
evolved  and  prolonged  outwards,  until  they  meet  an  involution  of  the  common  in- 
tegument, and  from  the  two  results  the  organ  of  sense.  The  sense  nerve  at  first 
seems  to  be  formed  by  the  contraction  of  the  evolved  tube,  forming  a  hollow  pedicle, 
but  is  subsequently  filled  up  with  nerve  fibres. 

One  other  difference  may  be  referred  to  in  connection  with  the  special  sense 

*  For  the  anatomy  of  the  brain  of  Myxinoid  Fishes,  see  Johannes  Muller,  Berlin  Trans.,  1837. 


40  ON   THE   NERVOUS    SYSTEM  IV. 

nerves ;  namely,  that  in  the  animal  series  they  are  never  seen  combined  with  motor 
roots,  are  never  presented  under  the  aspect  of  a  true  spinal  or  vertebral  nerve. 
It  has  been  maintained  by  Blainville  and  others,  that  the  motor  nerves  of  the  eye- 
ball are  the  nerves, "of  which  the  optic  is  the  sensitive  portion,  and  that  they  are 
separated  in  consequence  of  the  high  degree  of  specialization  of  function.  This 
assumption  is  readily  disproved  by  the  fact,  that,  of  these  same  motor  nerves,  the 
pathetic,  abducens,  and  some,  if  not  all,  of  the  branches  of  the  motor  communis,  can 
be  shown  to  be  dismemberments  of  the  trigeminus.  The  opinion  of  Oken,  which 
considers  the  special  sense  nerves  as  appendages  of  the  brain,  is  far  more  rational, 
and  has  the  merit  of  being  more  in  accordance  with  facts. 

Cranial  nerves  may  therefore  be  divided  into  two  groups  ;  namely,  into 

1.  Special  sense  nerves :  2.  Cranio-spinal  nerves : 

I.  Olfactory,  A.  Trigeminus, 

II.  Optic,  B.  Vagus, 

III.  Auditory  ;  C.  Hypoglossus  ; 

the  second  including  the  only  true  serial  repetitions  of  spinal  nerves. 

The  determination  of  the  typical  number  of  cranial  nerves  becomes  a  matter  of 
importance,  in  consequence  of  its  bearing  upon  the  philosophical  anatomy  of  the 
skull.  On  the  hypothesis  that  the  cranium  is  made  up  of  a  series  of  vertebrae, 
one  of  the  first  questions  which  is  presented  is  as  to  the  number  which  enter  into 
its  composition.  Throughout  the  vertebral  column,  as  ordinarily  understood,  the 
pairs  of  nerves  equal  the  number  of  vertebral  pieces.  If  the  cranium  is  reducible 
to  the  vertebral  type,  we  might  from  analogy  expect  that  there  would  be  found  a 
series  of  nerves  corresponding  in  number  to  the  vertebrae  of  which  the  cranium  is 
made  up.  If  we  admit  only  such  nerves  as  present  the  true  spinal  character  to  be 
indicative  of  the  number  of  vertebra?,  that  is,  those  which  have  motor  and  sensitive 
roots,  are  provided  with  ganglia,  and  have  a  similar  mode  of  development,  then, 
according  to  the  analysis  given  above,  there  being  three  pairs  of  nerves  conforming 
to  the  spinal  type,  we  should  infer  the  existence  of  three  vertebra. 

Anatomists,  however,  have  not  generally  followed  these  indications,  and  it  is  a 
singular  fact,  that,  in  establishing  the  number  of  cranial  vertebrae,  they  have  rested 
their  conclusions  on  such  widely  different  foundations.  Oken,  in  his  latest  pub- 
lication, admits  the  existence  of  four  vertebrae,  based  on  the  organs  of  sense  and 
the  lower  jaw,  and  which  he  designates  as  the  "  nose  vertebra,"  the  "  eye  vertebra," 
the  "ear  vertebra,"  and  the  "jaw  vertebra."  Bojanus  also  recognizes  four,  and 
substitutes  the  "  tongue  vertebra  "  for  Oken's  jaw  vertebra.  Agassiz  admitted  but  a 
single  cranial  vertebra,  since  the  chorda  dorsalis  of  the  embryo  did  not  extend  be- 
yond that  portion  of  the  base  of  the  skull  which  corresponds  with  the  basilar  portion 
of  the  occiput.  Professor  Owen,  the  most  recent  writer  on  the  subject,  who  has  inves- 
tigated it  very  minutely,  and  has  worked  out  his  system  with  admirable  skill,  bases 
his  vertebral  theory  upon  the  principal  subdivisions  of  the  encephalon,  from  which 
he  deduces  a  "  rhinencephalic,"  "  prosencephalic,"  "  mesencephalic,"  and  "  epen- 
cephalic  "  vertebra.  A  larger  number  has  been  admitted  by  others,  as  Geoffroy  St. 
Hilaire,  Carus,  and  Maclise,  based  mainly  on  an  unsound  determination  of  the 
different  osseous  elements. 


IV.  OF    HANA    PIPIENS.  41 

• 

If  we  apply  the  analogies  of  the  spinal  chord  and  vertebral  column  to  the 
cranium  and  its  nerves,  we  ought  to  base  our  determinations  on  the  repetitions  of 
true  spinal  nerves  and  of  the  true  vertebral  elements.  If  the  theory  be  true  which 
reduces  the  cranial  nerves  (exclusive  of  the  special  sense  nerves)  to  three,  namely, 
the  trigeminus,  vagus,  and  hypoglossus,  then  we  ought,  a  priori,  to  detect  at 
least  three  vertebral  segments.  This  conclusion  agrees  perfectly  well  with  the  deter- 
mination from  osteology.  For  the  larger  part  of  modern  anatomists  admit  at 
least  three  vertebrae,  though  some  admit  more,  but  are  not  precisely  agreed  as  to 
the  exact  number  of  elements  which  enter  into  the  composition  of  each.  These 
vertebrae  may  be  designated  as  follows :  1st,  the  occipital,  of  which  the  basilar 
bone  is  the  body ;  2d,  the  parietal,  of  which  the  posterior  sphenoid  is  the  body ; 
3d,  the  frontal,  of  which  the  anterior  sphenoid  is  the  body.  Professor  Owen  ad- 
mits a  fourth,  of  which  the  vomer  is  the  body,  and  as  this  vertebra  is  associated 
with  the  organs  of  smell,  he  designates  it  as  the  rhinencephalic  vertebra.  It  is 
through  or  between  these  three  vertebras  enumerated  above,  that  the  trigeminus, 
vagus,  and  hypoglossus  have  their  exit  from  the  cranial  cavity,  and  it  is  likewise 
through  or  between  these  same  vertebrae  that  the  special  sense  nerves  make  their 
escape.  If  the  number  of  pairs  of  nerves  of  both  kinds  is  to  regulate  the  num- 
ber of  vertebrae,  then,  instead  of  three  pairs,  we  must  admit  six  for  the  cranium 
alone,  leaving  wholly  out  of  view  the  face.  But  if  the  special  sense  nerves,  for 
reasons  already  stated,  can  be  rejected  as  indications  of  vertebra?,  the  cranio-spinal 
nerves  will  give  us  just  the  number  which  accords  with  osteology.  In  this  con- 
clusion we  are  supported  by  both  osteology  and  neurology.  Johannes  Muller 
admits  the  existence  of  three  vertebra?,  and  argues  from  them  the  number  of  pairs 
of  cranio-spinal  nerves.  "  According  to  my  view,  there  are  three  vertebral  nerves 
of  the  head,  just  as  there  are  three  cranial  vertebras.  The  first  is  the  fifth  or  tri- 
geminus, the  second  is  the  vagus  with  the  glosso-pharyngeal  and  accessory,  and  the 
third  is  the  hypoglossus." 

The  three-vertebra  theory  given  above  relates  simply  to  the  bones  constituting 
the  walls  of  the  cranial  cavity  which  include  the  brain  ;  no  account  is  taken  of 
the  jaws  and  other  bones  of  the  face,  nor  of  the  os  hyoides.  Professor  Owen,  in 
his  system,  regards  these,  with  the  scapular  arch,  as  forming  a  series  of  four  in- 
ferior or  "  haemal "  arches  to  the  four  cranial  vertebrae,  with  their  "  neural  arches," 
that  they  in  fact  are  serial  repetitions  of  ribs. 

It  would  be  foreign  to  the  purpose  of  this  paper  to  discuss  the  grounds  on  which 
these  conclusions  rest.  Another  hypothesis  seems  to  us  worthy  of  consideration, 
but  which  can  only  be  stated  in  general  terms,  as  follows.  The  teeth  in  the  early 
embryonic  conditions  are  developed  from,  and  are  dependences  of,  the  mucous 
membrane  of  the  mouth ;  in  many  Fishes  these  conditions  are  permanent ;  in  Hays, 
Sharks,  and  other  cartilaginous  Fishes,  the  jaws  or  other  bones  which  support 
teeth  are  equally  developed  in  the  internal  integument  or  mucous  membrane, 
and  are  never  closely  connected  with  the  cranium  except  by  ligament ;  the  hyoid 
apparatus  is  likewise  developed  in  the  walls  of  the  alimentary  canal.  If  to  these 
facts  we  add  another,  namely,  that  primarily  the  mouth  and  nostrils  form  a  single 


42  ON    THE    NERVOUS    SYSTEM  IT. 

cavity,  and  are  only  separated  after  development  has  advanced  to  a  certain  stage, 
we  have  a  strong  ground  for  the  hypothesis,  that  all  the  bones  of  the  face  which 
are  developed  in  the  walls  of  the  primitive  cavity  of  the  mouth  which  they  sur- 
round, are  in  their  anatomical  and  physiological  relations  splanchnic,  connected 
either  with  digestion  or  respiration,  rather  than  parts  of  the  endo-skeleton  of 
animal  life. 

The  conclusions  which  have  been  drawn  from  the  statements  made  above  are  as 
follows :  that  in  Frogs  the  vagus  comprises  the  glosso-pharyngeal  and  accessory 
nerves  ;  that  the  trigeminus  comprises  the  facial,  the  abducens,  and  in  the  Salaman- 
ders the  patheticus  and  portions  of  the  motor  communis  ;  that  other  evidence 
sustains  the  hypothesis,  that  the  whole  of  the  motor  communis  is  a  dependence  of 
the  trigeminus ;  if  to  these  we  add  the  hypoglossus  (which  in  Frogs  is  exceptionally 
a  spinal  nerve),  we  shall  have  three  pairs  of  cranial  nerves,  each  having  all  the 
characters  of  a  common  spinal  nerve,  namely,  motor  and  sensitive  roots  and  a 
ganglion ;  that  there  are  no  nerves  to  indicate  a  fourth  vertebra,  unless  the  special 
sense  nerves  are  considered;  if  these  are  admitted  as  indications,  then  we  must 
presuppose  either  two  pairs  of  nerves  to  each  vertebra,  or  the  existence  of  six 
vertebrae,  which  is  a  larger  number  than  can  be  accounted  for  on  an  osteological 
basis.  The  functions  and  mode  of  development  of  the  special  sense  nerves  we 
have  taken  as  affording  sufficient  grounds  for  considering  them  as  of  a  peculiar 
order,  and  not  to  be  classified  with  common  spinal  nerves. 

SECTION  VI.  —  SPINAL  NERVES. 

I.  Hypoglossus.  (Plate  I.  Fig.  1,1.)  —  Another  remarkable  feature  in  the  nervous 
system  of  Frogs,  and  one  which  has  been  noticed  in  other  tailless  Batrachians  also, 
is  the  fact  that  the  hypoglossal  nerve  (the  ninth  pair  of  Willis,  and  the  eleventh 
of  Soemmering),  is  not,  as  in  most  Vertebrates,  one  of  the  cranial  nerves,  but  the 
first  of  the  dorsal  or  true  spinal  series.  Its  origin  is  at  the  extreme  portion  of  the 
medulla  oblongata,  just  in  front  of  the  contraction  of  the  chord  which  precedes 
the  brachial  enlargement.  In  reference  to  the  determination  of  its  true  affinities, 
it  is  of  consequence  to  notice  the  fact,  that  it  is  provided  with  two  kinds  of  roots, 
of  which  the  anterior  or  motor  are  the  most  numerous,  consisting  of  a  bundle  of 
filaments  attached  a  little  nearer  to  the  median  line  than  the  corresponding  ones 
from  the  vagus.  The  posterior  or  sensitive  root  is  quite  small  and  scarcely  per- 
ceptible ;  it  does  not  appear  to  have  been  noticed,  except  by  Volkman.  Its  minute- 
ness is  such,  that  in  removing  the  membranes,  unless  especial  care  be  taken,  it  will 
be  torn  away  with  them,  and  therefore  easily  escape  detection.  The  presence  of  this 
dorsal  or  sensitive  root  serves  to  identify  it  with  a  true  spinal  nerve ;  and  the  iden- 
tification is  rendered  complete  by  the  existence  of  a  minute  ganglion  near  its 
junction  with  the  motor  root.  The  two  kinds  of  root  fibres,  just  after  escaping 
from  the  spinal  canal  between  the  first  and  second  vertebrae,  unite  and  form  a 
single  trunk,  which  almost  always  is  provided  with  a  small  sacculated  appendage 
filled  with  calcareous  crystals.  The  trunk  of  the  nerve  descends  along  the  sides 


IV.  OF    RANA    PIPIENS.  43 

of  the  neck,  crosses  the  vagus  and  its  laryngeal  branch,  and,  running  nearly  paral- 
lel to  the  glosso-pharyngeal,  passes  along  the  genio-hyoid  muscle  as  far  as  the 
symphysis  of  the  lower  jaw ;  it  then  ascends,  in  company  with  the  last-mentioned 
nerve,  into  the  substance  of  the  tongue,  and  is  lost  among  its  muscular  fibres.  This 
description  applies  to  the  principal  trunk ;  in  its  progress,  however,  it  gives  off  nu- 
merous branches,  repeating  very  nearly  the  distribution  of  the  same  nerve  in  the 
human  body ;  in  other  words,  it  is  distributed  to  the  muscles  which  move  the  os 
hyoides  and  tongue.  The  following  branches  were  traced :  1st,  a  branch  to  the 
muscles  attached  to  the  vertebral  column  in  its  immediate  neighborhood  and  to  the 
omo-hyoid ;  2d,  to  the  sterno-hyoid ;  3d,  to  the  hypoglossus ;  4th,  genio-hyoid  ; 
5th,  genio-glossus.  Galvanism  proves  still  further  the  relation  of  these  muscles  to 
the  hypoglossal  nerve ;  if  this  agent  be  applied  to  the  main  trunk  near  the  verte- 
bral column,  convulsions  are  simultaneously  produced  throughout  the  whole  hyoid 
and  glossal  group ;  but  nothing  of  the  kind  is  noticed,  as  has  already  been  stated, 
when  it  is  applied  to  the  glosso-pharyngeal,  which  has  a  direction  so  nearly  parallel 
with  it.*  On  entering  the  base  of  the  tongue,  the  hypoglossus,  like  the  glosso- 
pharyngeal,  is  thrown  into  zigzag  folds,  which  adapt  it  to  the  peculiar  extensibility 
of  that  organ. 

The  descriptions  of  this  nerve  by  different  anatomists  are  somewhat  discordant, 
and  it  is  therefore  a  matter  of  some  interest  that  they  should  be  compared.  Vogt, 
in  the  memoir  already  referred  to,  says :  "  Volkman  describes  this  nerve  as  the  first 
nerve  of  the  neck,  which  it  is  according  to  its  exit,  but  not  according  to  its  origin 
and  its  course.  He  also  represents  its  origin  as  at  some  distance  from  the  vagus,  and 
the  nerve  as  if  it  were  provided  with  a  ganglion.  I  thought  I  could  at  least  find  the 
last  in  Frogs,  but  was  soon  convinced  of  my  error."  "  The  hypoglossus  takes  its  origin 
close  to  the  vagus,  but  nearer  to  the  median  line,  from  the  under  surface  of  the 
medulla  oblongata,  and,  instead  of  going  directly  outwards,  bends  backwards  close 
to  the  under  side  of  the  medulla  within  the  pia  mater,  and  when  opposite  to  the 
foramen  makes  a  sudden  bend  outwards,  so  that,  if  the  pia  mater  is  untouched,  it 
has  the  appearance  of  having  its  origin  opposite  to  the  hole,  and  at  some  distance 
from  the  vagus.  Has  Volkman  been  deceived  by  this  disposition  1 "  "  That,  as 
Volkman  says  it  does  in  Frogs,  it  takes  its  origin  with  two  roots,  and  has,  as  he 
draws  it,  a  ganglion,  is  certainly  not  the  case  in  Toads,  and  I  believe  that  no  error 
on  my  part  exists."  Stannius  distinctly,  but  incorrectly,  asserts,  that  the  hypo- 
glossus has  no  posterior  roots.  "  The  spinal  nerves  always  arise  by  two  roots ;  the 
first  two  cervical  nerves  appear  to  form  an  exception  to  this  rule,  not  only  in  the 
naked  Reptiles,  where  they  take  the  place  of  the  hypoglossus,  but  also  in  some  of 
the  scaly  ones."  f 

According  to  the  dissections  which  form  the  basis  of  this  memoir,  Volkman's 
description  is  quite  correct,  both  as  to  the  existence  of  two  kinds  of  roots  and  of 
the  ganglion ;  also  as  to  the  position  on  the  side  of  the  medulla.  The  roots  of  the 

*  The  same  result,  as  regards  its  function,  is  shown  by  the  experiments  of  Dr.  Waller. —  Philosophical 
Transactions,  1850. 

t  Stannius,  Manuel  d'Anatomie  Comparee,  Tom.  II.  p.  200. 


44  OX    THE    NERVOUS    SYSTEM  IV. 

hypoglossus  are  in  part  connected  by  the  arachnoid.     In  Bufo  America-mis  I  have 
found  the  hypoglossus  arising  very  nearly  as  Vogt  has  described  it. 

Vogt's  classification  of  this  nerve  among  the  true  cranial  nerves  does  not  seem  to 
be  satisfactorily  sustained,  and  certainly  will  not  hold  as  regards  Frogs.  In  them  it 
certainly  has  all  the  characters  of  a  common  spinal  nerve ;  viz.  two  kinds  of  roots,  a 
ganglion  on  one  of  them,  a  mass  of  crystals  attached  as  in  the  spinal  nerves,  and 
making  its  exit  at  an  intervertebral  foramen.  There  is  still  another  anatomical 
character,  though  perhaps  not  an  important  one,  which  allies  it  to  the  spinal  more 
than  the  cranial  nerves  ;  this  is  the  primitive  direction  of  the  nerve  roots  back- 
wards instead  of  forwards,  as  is  the  case  with  the  cranial  nerves. 

II.  Brachial  Nerves.     (Plate  II.  Figs.  1,  2.)  —  These  are  comparatively  simple. 
In  most  t>f  the  higher  Reptiles  which  have  limbs,  they  consist  of  three  or  more  pairs, 
which  subsequently  unite  and  form  the  brachial  plexus,  which  in  turn  gives  its 
branches  to  the  upper  extremity.     In  Frogs,  however,  only  a  small  filament  is  given 
by  the  third  spinal  to  the  brachial  nerve,  and  thus  an  approach  merely  to  a  bra- 
chial plexus  exists.     All  the  nerves  to  the  arms,  with  the  exception  of  the  above- 
mentioned  branch,  are  supplied  by  the  single  trunk  of  the  second  pair,  which  is  at- 
tached to  the  spinal  chord  by  several  distinct  motor  and  sensitive  filaments.     The 
trunk  passes  to  the  upper  part  of  the  arm  before  it  divides,  giving  off,  however, 
collateral  branches  to  the  muscles  of  the  scapular  and  clavicular  regions ;  also  a 
branch  to  the  pectoral  muscles  and  a  circumflexus  humeri.     The  remaining  por- 
tion of  the  nerve  forms  the  ulnar  and  radial  branches. 

III.  IV.  V.  VI.  are  the  smallest  pairs  of  the  spinal  nerves.     They  all  arise  by 
single  anterior  and  posterior  roots,  and  are  mainly  distributed  to  the  muscles  and 
skin  of  the  back  and  the  abdomen.     The  distribution  of  the  cutaneous  nerves  will, 
however,  be  described  hereafter. 

Lumbar  Nerves,  VII.  VIII.  IX.  These  likewise  all  arise  by  single  anterior  and 
posterior  roots  from  the  spinal  chord,  but  they  are  very  much  longer  than  those  of 
the  preceding  pairs,  in  consequence  of  the  greater  distance  of  their  origins  from 
the  intervertebral  foramina,  where  the  anterior  and  posterior  filaments  unite.  The 
three  lumbar  nerves  thus  formed  descend  to  the  neighborhood  of  the  hip  joint, 
where  the  eighth  and  ninth  pairs  become  intimately  blended  (c),  and  at  the  same  time 
receive  an  anastomosing  branch  from  the  seventh  (b).  After  giving  off  the  branch  just 
referred  to,  the  seventh  pair  makes  a  turn  outwards  and  upwards,  so  as  to  give  its 
terminal  filament  to  the  posterior  walls  of  the  abdomen ;  from  the  convex  side  of 
its  curved  portion  are  given  off  numerous  branches,  which  descend  in  a  parallel 
series  and  are  distributed  to  the  skin  of  the  thigh  (g).  This  nerve,  from  the  fact  that 
it  escapes  at  the  inguinal  region,  and  in  consequence  of  its  distribution  to  the  leg, 
may  be  regarded  as  identical  with  the  cruralis. 

By  the  union  of  the  eighth  and  ninth,  with  a  portion  of  the  seventh,  a  large 
sciatic  trunk  is  formed,  and  this  descends  nearly  to  the  knee  without  division, 
giving  off,  however,  as  collateral  branches,  a  glutasal  nerve  (e),  and  two  larger 
muscular  nerves  to  the  thigh  (/).  At  the  knee  the  sciatic  is  divided  into  two 
branches,  the  tibial  and  peroneal  nerves  (h  and  i). 


IV.  OF    RAN  A   PIPIENS.  45 

X.  Coccygeal  Nerve ;  10.  This  is  the  last  of  the  series  of  spinal  nerves,  and 
from  its  minuteness  does  not  appear  to  have  attracted  notice ;  consequently,  the 
number  of  pairs  is  usually  enumerated  as  nine.  It  is  most  easily  detected  on 
either  side  of  the  coccyx  beneath  the  muscles  extending  from  it  to  the  ilia.  If 
traced  from  its  termination  towards  the  chord,  it  will  be  found  entering  the 
cavity  of  the  coccyx  by  a  foramen  pierced  quite  obliquely  in  its  walls  at  a  short 
distance  from  the  anterior  extremity  of  the  bone.  This  nerve  is  attached  to  the 
chord  by  both  kinds  of  roots,  just  beyond  the  third  crural  or  ninth  pair  of  spinal 
nerves.  The  detection  of  this  nerve  has  especial  interest,  since  it  demonstrates 
conclusively  the  homology  of  the  anomalous-shaped  coccyx  with  a  true  vertebra, 
and  also  makes  the  number  of  nerves  and  vertebral  pieces  equal. 

Cutaneous  Branches  of  the  Spinal  Nerves.  —  The  skin  of  Frogs,  it  will  be  remem- 
bered, is  attached  only  to  a  very  limited  extent  to  the  parts  beneath,  so  that  there  is 
a  series  of  large  subcutaneous  cavities,  which  are  for  the  most  part  separated  from 
each  other.  The  first  or  dorsal  subcutaneous  cavity  covers  the  whole  region  of  the 
back,  extending  from  the  occiput  to  the  posterior  part  of  the  trunk,  and  limited  on 
the  sides  by  the  union  of  the  skin  with  the  muscles  beneath,  on  a  line  extending 
from  behind  the  eyes  as  far  as  the  pelvis.  The  lateral  cavities,  one  on  each  flank, 
are  limited  by  the  lines  described  above,  and  two  others,  one  on  each  side,  extending 
from  the  axilla  to  the  pelvis.  The  fourth  or  abdominal  cavity  is  comprised  be- 
tween the  two  last,  and  extends  over  the  whole  abdominal  region. 

The  cutaneous  nerves  escape  through  the  muscles  to  the -skin,  mainly  in  three 
directions ;  namely,  on  each  side  of  the  median  line  on  the  back,  and  at  the  upper 
and  lower  lines  which  limit  the  lateral  subcutaneous  cavities.  The  dorsal  branches 
are  in  pairs,  nine  in  number,  and  corresponding  with  the  first  nine  vertebra?.  In 
front  of  the  scapula  is  a  minute  branch  of  this  series,  which  is  derived  from  the 
hypoglossus,  and  to  this  same  series  should  be  added  the  cutaneous  filament  from 
the  vagus  distributed  to  the  skin  near  the  occiput.  On  the  upper  lateral  line  eight 
pairs  are  given  to  the  skin ;  on  the  sides  in  the  lateral  cavity  five  pairs  descend  to 
the  lower  lateral  line,  where,  with  three  others  given  eff  more  posteriorly,  they 
enter  the  skin.  These  last  branches  seem  to  be  the  ones  liable  to  the  greatest  irreg- 
ularity. The  existence  of  a  dorsal  cutaneous  branch  from  the  vagus  and  hypoglos- 
sus both,  added  to  the  facts  already  stated  under  another  head,  go  still  further  to 
show  their  identity  with  common  spinal  nerves. 

Crystal  Capsules  attached  to  the  Spinal  Nerves.  (Plate  I.  Fig.  1,  i,  i.)  —  The  exist- 
ence of  certain  white  bodies  on  either  side  of  the  vertebral  column  in  Frogs  seems 
for  a  long  time  to  have  attracted  attention.  They  are  referred  to  by  Blasius,  in  his 
Anatome  Animalium,*  and  are  figured  by  Swann,j-  though  he  gives  no  descriptions. 
Wagner  mentions  them  as  follows  :  —  "  The  ganglia  admit  of  being  very  readily 

*  "  Ab  utraque  spinalis  medullas  parte,  substantia  qua?dam  albicans  calcis  instar  adhaerescit,  quam  vasa 
plurima  perreptant ;  substantia  hacc  sail  volatili  est  analoga,  cum  ex  observatione  Swammerdammii 
affuso  spirito  acido  effervescat.  Cui  usui  tot  vasorum  plexibus  inserviat  admodum  obscurum  est."  — 
Gerardi  Blasii  Anatome  Animalium,  Amstellodami,  1681,  p.  291. 

t  Comp.  Anat.  Nerv.  Syst.,  Plate  VII.  Figs.  5,  6. 

7 


46  ON    THE   NERVOUS    SYSTEM  IV. 

demonstrated,  lying  upon  the  sides  of  the  vertebral  column ;  they  are  situated  near 
those  small  white  vesicles,  which  protrude  by  becoming  swollen,  chiefly  during 
the  spring  of  the  year,  and  contain  numerous  microscopic  calcareous  crystals."  * 
Stannius  describes  them  as  an  accumulation  of  the  white  substance  which  covers 
the  pia  mater  around  the  nerves  where  they  escape  from  the  spinal  canal,  and 
which,  under  the  microscope,  has  the  appearance  of  a  mass  of  crystals,  f  Professor 
Owen  has  usually  called  attention  to  them  in  his  annual  Hunterian  lectures,  though 
he  has  published  nothing  in  relation  to  them. 

As  I  have  seen  them  in  dissections,  they  are  subject  to  some  variety,  but  exist  on 
the  trunks  of  all  the  true  spinal  nerves,  the  hypoglossus  included,  and  invest  them 
more  or  less  completely  at  their  exit  from  the  spinal  canal,  occupying  the  space  be- 
tween the  transverse  processes  of  two  adjoining  vertebra;.  The  capsule  is  a  very 
thin  membrane,  sometimes  having  a  diameter  of  two  or  three  lines ;  its  surface  is 
minutely  lobulated,  an  appearance  which  results  from  the  existence  of  numerous 
partitions  within,  forming  many  small  cavities,  which  communicate,  though  not 
very  freely,  with  each  other.  The  contents  of  these  pouches  are  vast  numbers  of 
exceedingly  minute  crystals  of  a  somewhat  oval  form  (Plate  I.  Fig.  18),  pointed 
at  their  extremities,  and  comparable  in  shape  to  a  lemon-seed,  but  sometimes  pre- 
senting well-defined  angles. 

These  capsules  are  not  in  any  definite  proportion  to  the  size  of  the  nerves  to 
which  they  are  attached,  those  of  the  brachial,  for  example,  which  is  one  of  the 
largest  pairs  of  nerves,  being  much  smaller  than  those  connected  with  the  dorsal 
nerves,  which  are  of  less  size.  As  to  the  statement  by  Wagner,  that  they  are 
found  more  swollen  in  the  spring,  this  condition  has  not  been  noticed  in  the  in- 
stances which  have  fallen  under  my  observation.  I  have  detected  them  of  nearly 
equal  dimensions  at  all  seasons  of  the  year,  whether  examined  in  spring,  summer, 
late  in  the  autumn,  or  even  in  midwinter.  They  do  not  belong  exclusively  to  the 
adult  period,  but,  as  stated  by  Stannius,  I  have  found  them  in  the  larva?  at  different 
periods,  even  before  the  development  of  arms  and  legs.  Dissections  of  other  than 
lianiform  Batrachians  have  not  led  to  their  detection ;  I  have  not  found  them  in 
Siren,  Menobranchus,  Bufo,  or  Salamandra,  but  have  seen  them  in  Rana  fontinalis, 
R.  halecina,  and  R.  palustris.  They  seem  to  be  in  these  species  constant  appen- 
dages to  the  spinal  nerves.  The  crystals  which  these  capsules  include  are  similar  in 
size  and  form  to  those  contained  in  the  vestibule  of  the  ear ;  in  the  latter  case  they 
are  in  contact  with  the  extremity  of  the  nerve,  but  in  the  former  they  are  simply 
attached  to  its  sheath. 

SECTION  VII.  —  SYMPATHETIC  NERVE. 

The  small  number  to  which  pairs  of  spinal  nerves  are  reduced  involves,  as  a  mat- 
ter of  course,  a  sympathetic  nerve  of  a  corresponding  degree  of  simplicity.  It  is 
connected  with  all  of  the  nerves  from  the  trigeminus  to  the  third  lumbar  nerve  in- 

*  Comp,  Anat.  Verteb.,  Part.  I.  p.  151.  t  Manuel  d'Anat.  Comp.,  Tom.  II.  p.  200. 


IV. 


OF    RANA   PIFIENS. 


47 


Fig.  4. 


>  „ 


elusive ;  at  its  anterior  extremity,  no  filament  was  traced  to  the  motor  communis, 
though  analogy  would  lead  us  to  expect  one ;  nor  at  the  other  extremity  was  any 

traced  to  the  coccygeal  pair.  The  filament  from  the 
ganglion  of  the  trigeminus  to  the  vagus  is  very  mi- 
nute, and,  as  will  be  seen  by  reference  to  the  figure, 
no  sympathetic  ganglion  is  developed  upon  it.  Pre- 
cisely similar  conditions  exist,  according  to  Fischer, 
in  Bombinator  igneus,  Pelobates  fuscus,  and  Hyla 
arborea  ;  also,  according  to  Vogt,  in  Bufo  panlheri- 
nus.  From  the  posterior  extremity  of  the  vagal 
ganglion,  the  nerve  extends  backwards  as  far  as 
the  fourth  dorsal,  receiving  filaments  from  the  hy- 
poglossal,  brachial,  and  the  two  succeeding  spinal 
nerves,  and  where  each  of  these  filaments  joins  the 
sympathetic  trunk,  a  distinct  ganglion  is  formed. 
After  it  receives  its  fibres  from  the  fourth  spinal 
nerve,  it  is  enlarged,  leaves  the  side  of  the  verte- 
bral column,  and  forms,  with  the  nerve  from  the 
opposite  side,  a  plexus  around  the  mesenteric  artery, 
from  which  it  is  distributed  to  the  spleen,  stomach, 
and  intestines. 

The  branches  of  the  fifth  and  sixth  pairs  unite 
and  form  a  ganglion,  from  which  a  small  branch 
goes  to  the  splanchnic  plexus,  and  another  back- 
wards to  the  ganglion  of  the  next  nerve  (seventh), 
which  is  the  first  of  the  crural  or  lumbar  pairs  ; 
this  last  ganglion  in  turn  sends  a  branch  back 
to  the  ganglia  of  the  eighth  and  ninth  pairs, 
e,  e,  e.  The  filaments  given  off  from  the  group 
just  mentioned  are  distributed  almost  entirely 
to  the  kidneys  and  neighboring  viscera,  follow- 
ing the  course  of  the  bloodvessels  which  ramify 
upon  them. 

It  is  seldom  that  we  have  a  more  favorable  op- 
portunity offered  for  studying  the  minute  structure 
of  the  ganglia  than  in  the  sympathetic  system  of 
Frogs,  where  they  are  both  small  and  transparent.  I  have  not  been  able  to  deter- 
mine any  thing  different  from  what  was  previously  known  with  regard  to  their 
minute  structure.  Fig.  10,  Plate  II.  represents  the  ganglion  just  behind  the  third 
spinal  nerve ;  a,  b  is  the  principal  trunk  of  the  nerve ;  c  is  the  sympathetic 
branch  ;  d,  d,  the  sympathetic  trunk  in  front  of  and  behind  the  ganglion.  Some  of 
the  fibres  of  the  sympathetic  pass  through  the  ganglion  without  separating ;  others, 
leave  the  principal  fasciculus,  and  become  more  or  less  mixed  up  with  the  nerve 

Ti  .       •          •     ,       ,1         Ij.: ~£   tV,«    ™ov.«.i;/->n         rPV>o   Viranr>Vi    f  rliviflps  into  t.WO 


e-- 


V.  Trigeminus. 

VI.  Auditory  nerve. 
VII.  Vagus. 

a  and  6.    Right  and  left  aortas  at  their  onion 
e.    Mesenteric  artery. 

d.  Descending  aorta. 

e,  e.  e.    Renal  and  genital  ganglia. 


cells  entering  into  the  composition  of  the  ganglion.    The  branch  c  divides  into  two 


48  ON    THE   NERVOUS    SYSTEM    OF    RANA    PIPIENS.  IV. 

principal  fasciculi,  one  of  which  goes  towards  the  head,  and  the  other  backwards ; 
but  some  of  the  same  fibres  leave  the  principal  bundles  and  run  irregularly 
among  the  cells.  The  sympathetic  nerve  fibres  are  more  minute  than  the  spinal, 
and  some  of  the  latter  may  be  readily  traced  into  the  sympathetic,  where  they  are 
distinguished  by  their  size.  A  portion  of  the  root  c  is,  however,  made  up  of  the 
more  minute  sympathetic  fibres.  The  ganglion  cells  are  well  defined,  lightly 
pressed  together,  so  that  their  spherical  form  is  but  slightly  interfered  with,  and 
contain  a  few  granules  of  a  yellowish  color.  In  no  instance  was  a  caudate  cell 
noticed,  nor  any  connection  between  the  cells  and  the  nerve  tubes.  The  latter 
passed  among,  but  not  into,  the  cells.  Each  ganglion  formed  by  the  union  of  the 
spinal  and  sympathetic  nerve  may  therefore  be  described  as  consisting  of  the  fol- 
lowing elements :  1st,  a  mass  of  ganglion  cells ;  2d,  a  fasciculus  of  sympathetic 
fibres,  some  of  which  last  become  detached  from  the  principal  bundle,  and,  after 
passing  irregularly  among  the  cells,  either  return  to  the  fasciculus  from  which  they 
came,  or  join  one  of  the  other  fasciculi;  3d,  a  double  series  of  filaments  from  a 
spinal  nerve,  one  series  passing  forwards  and  the  other  backwards ;  some  of  the 
fibres  of  each  series  become  detached  from  their  fasciculi,  and  pass  irregularly 
among  the  ganglion  cells. 

Besides  these  ganglia  connected  with  the  spinal  nerves,  others  more  minute 
appear  to  be  formed  wherever  two  sympathetic  branches  cross  each  other,  in  which 
case  the  fibres  of  the  different  fasciculi  separate  and  form  an  open  but  irregular 
series  of  meshes,  in  which  ganglion  cells  are  deposited.  In  the  formation  of  each 
ganglion,  it  seems  to  be  a  general  rule  that  there  is  an  interchange  of  filaments 
between  the  two  or  more  trunks  which  enter  into  its  formation ;  also  a  deposit  of 
ganglion  cells  in  the  meshes  formed  by  the  separated  fibres.  In  this  last  respect  it 
differs  from  a  plexus,  which  consists  merely  in  the  interchange  of  filaments  of  two 
adjoining  nerves,  without  any  deposit  of  nerve  or  ganglion  cells. 

From  what  has  been  stated  with  regard  to  the  relation  of  nerve  tubes  and  nerve 
cells  in  the  brain,  in  the  spinal  chord,  and  sympathetic,  it  seems  almost  certain  that 
continuity  of  structure  between  the  two  histological  elements  of  the  nervous  sys- 
tem is  in  the  species  here  described  not  essential  to  nervous  action.  The  only 
conditions  which  direct  observation  gives  evidence  of  is  close  proximity,  but  not 
absolute  continuity. 


EXPLANATION    OF    THE    PLATES. 


PLATE  L 

IN  Figs.  1  to  9  inclusive,  corresponding  parts  are  indicated  by  the  same  letters. 

Olfactory  Lobes  A. 

Cerebral  Lobes  B. 

Corpora  Striata  C. 

Optic  Thalami  D. 

Pineal  Body  E. 

Pituitary  Body  F. 

Optic  Lobes  G. 

Cerebellum  H. 

FIG  1.  Cerebro-spinal  axis  seen  from  beneath,  enlarged  four  times,  linear  measurement,  showing  the 
origins  of  the  cranial  and  spinal  nerves. 

I.  Olfactory  nerve  ;  II.  Optic  nerve  ;  III.  Motor  communis  ;  IV.  Patheticus  ;  V.  Trigeminus. 

a,  portio  dura,  or  facial,  which  joins  the  ganglion  of  the  trigeminus  ;  J,  motor  externus  or  abducens, 
which  also  joins  the  ganglion  of  the  trigeminus;  c,  "  facial,"  a  nerve  formed  by  the  union  of  a  branch 
from  the  trigeminus  with  another,  d,  from  the  vagus. 

VI.  Auditory  nerve. 

VII.  Vagus,     d,  branch  joining  the  "  facial  "  ;  e,  motor  root ;  /,  cutaneous  branch  ;  g,  h,  glosso-pha- 
ryngeal. 

I.  First  enlargement,  or  medulla  oblongata. 

L.  Brachial  enlargement. 

N.  Lumbar,  or  crural  enlargement. 

0.  Coccygeal  portion. 

1,  i.  Crystal  capsules  connected  with  all  of  the  spinal  nerves,  except  the  tenth  pair. 
k,  k.  Ganglia  of  the  spinal  nerves. 

FIG.  2.  Dorsal  view  of  the  cerebro-spinal  axis,  enlarged  two  diameters,  linear  measurement.  A,  B,  D, 
E,  G,  H,  the  same  as  in  Fig.  1.  K,  fourth  ventricle.  L,  posterior  pyramidal  tract,  enlarged  at  each 
of  the  bulgings  of  the  chord  ;  the  posterior  pyramids  form  a  similar  enlargement  for  the  medulla  oblon- 
gata, but  are  separated  by  the  fourth  ventricle. 

FIG.  3.  Side  view  of  the  cerebro-spinal  axis.  Letters  indicate  the  same  parts  as  in  the  preceding 
figures. 

FIG.  4.  Brain  and  spinal  chord  of  Bufo  Americanus.     References  as  before. 

FIG.  5.  Brain  of  Menolrranchus  lateraUs.  The  optiolobes,  G,  are  fused,  as  in  Menopoma,  and  as  are 
the  olfactory  lobes  in  Frogs  and  the  cerebral  lobes  in  some  Plagiostome  Fishes. 

FIG.  6.  Transverse  section  of  the  brain,  showing  the  cavities  of  the  olfactory,  cerebral,  and  optic  lobes. 


50  ON    THE    NERVOUS    SYSTEM  IV. 

FIG.  7.  Longitudinal  section  of  the  brain,  a  little  to  the  left  of  the  median  line.  The  corpus  striatum, 
C,  is  here  exposed  to  view,  also  the  body  within  the  optic  lobes,  G. 

FIG.  8.  Longitudinal  section  of  the  same  on  the  median  line ;  the  cut  surfaces  are  shaded.  L  is  the 
entrance  to  the  lateral  ventricle,  and  the  space  between  this  opening  and  the  olfactory  lobes,  A,  indicates 
the  extent  of  the  fissure  which  extends  from  the  upper  to  the  under  surface,  completely  separating  the 
cerebral  lobes  from  each  other. 

FIG.  9.  A  plan,  showing  the  connection  between  the  spinal  chord  and  the  different  portions  of  the  brain. 
FIG.  10.  Nerve  cells  or  vesicles  from  the  cerebral  lobes. 

FIG.  11.  Pineal  body,  consisting  almost  wholly  of  loops  of  bloodvessels  ;  the  whole  surface  is  covered 
with  cilated  epithelium,  as  at  a. 

FIG.  12.  A  small  portion  of  the  pineal  body,  magnified,  showing  an  inclosed  loop  of  bloodvessel,  and 
the  epithelial  covering. 

FIG.  13.  A  small  portion  of  chord  from  the  median  line,  showing  the  nerve  tubes  which  pass  from  one 
side  to  the  other  in  the  gray  substance. 

FIG.  14.  A  small  portion  of  the  chord  highly  magnified,  showing  the  entrance  of  one  of  the  roots  of  a 
spinal  nerve,  as  seen  on  the  surface. 

FIGS.  15  and  16.  Portions  of  the  chord  from  the  tail  of  a  tadpole,  showing  the  existence  of  a  central 
mass  of  cells  with  white  columns  on  each  side  ;  the  nerve  roots  enter  these  last,  and  ascend  towards  the 
trunk.  A  few  transverse  fibres  only  are  seen. 

FIG.  17.  The  under  surface  of  the  lower  jaw,  and  sublignal  region  of  a  Frog.  M,  lower  jaw;  V  and 
V,  branches  of  the  facial  portion  of  the  trigeminus  ;  the  same  as  i,  k,  and  h,  Fig.  2,  Plate  II. 

FIG.  18.  Calcareous  crystals  from  the  crystal  capsules  of  the  spinal  nerves. 


PLATE    II. 

'  FIG.  1.  General  view  of  the  spinal  nerves,  of  the  natural  size.  2,  brachial  nerves,  a,  anastomosing 
filament  from  the  third  spinal  nerve,  forming  a  simple  brachial  plexus.  The  three  following  nerves  are 
distributed  to  the  walls  of  the  abdomen.  7,  8,  9,  lumbar  nerves  ;  c,  union  of  the  8th  and  9th  with  a 
branch  from  the  7th,  forming  the  single  sciatic  trunk  ;  e,  gluteal  nerve  ;  /,  nerve  to  muscles  of  the  thigh  ; 
g,  branches  of  the  crural  nerve,  distributed  to  the  skin  of  the  thigh ;  A,  tibial,  and  i,  peroneal  nerves. 

FIG.  2.  Some  of  the  details  of  the  distribution  of  the  trigeminus  (V.)  and  vagus  (VII.)  nerves,  a,  or- 
bitar  branch  of  trigeminus  ;  J,  palatine  branch  ;  c,  terminal  branches  to  vomerine  teeth  and  internal  nasal 
opening  ;  d,  anastomosing  branch  to  upper  maxillary  nerve  ;  e,  upper  and  lower  maxillary  nerves  united  ; 
g,  "  facial,"  formed  by  the  union  of  a  branch  from  the  trigeminus  and  vagus  nerves  ;  A,  tympanic  branch  ; 
t,  jugular  branch  ;  k,  lower  jaw  branch ;  the  last  two  are  the  same  as  V  and  V,  Plate  I.  Fig.  17 ;  /,  n, 
branch  of  vagus  to  heart,  lungs,  and  stomach  ;  m,  glosso-pharyngeal. 

FIG.  3.  Side  view  of  the  branches  of  the  trigeminus.  a,  orbitar  branch  ;  J,  palatine  branch  ;  c,  fila- 
ments to  inner  nasal  orifice  ;  d,  union  of  palatine  and  upper  maxillary  branches  ;  e,  upper  maxillary 
nerve  ;  /,  lower*maxillary  nerve  ;  g,  "  facial." 

FIG.  4.  Right  eye  seen  from  above.  III.  Motor  communis  entering  superior  and  internal  rectus  mus- 
cles. IV.  Patheticus  distributed  to  the  superior  oblique  muscles.  V*.  (on  the  left  of  the  figure),  orbitar 
branch  of  trigeminus  (should  be  marked  V.)  ;  V'.  (on  the  right),  the  alducens,  which  is  a  branch  of 
the  trigeminus,  distributed  to  the  external  rectus. 

FIG.  5.  IV.  Patheticus.  V.  Orbitar  branch  of  the  trigeminus,  from  which  a  filament  is  given  off,  cross- 
ing the  preceding,  and  which  appears  to  communicate  with  it. 


IV.  OF    RAN  A    PIPIENS.  51 

FIG.  6.  Right  eye  seen  from  below.  III.  Motor  communis  giving  branches  to  rectus  inferior  and  rectus 
internus,  also  to  the,  obliquus  inferior  muscles.  V.  Branch  of  trigeminus  to  the  external  rectus,  abducens. 

FIG.  7.  Tadpole,  showing  general  form  of  the  chord  previous  to  the  development  of  legs. 

FIG.  8.  Tadpole,  showing  changes  in  the  form  of  the  chord  after  the  development  of  the  legs  and 
before  the  absorption  of  the  tail. 

FIG.  9.  Tadpole,  showing  the  temporary  branches  of  the  vagus  ;  a,  branch  of  vagus  giving  off  dorsal 
branch,  b,  distributed  to  the  fin  of  the  tail,  and  the  lateral  nerve,  c  ;  d,  branches  of  vagus  passing  along 
the  branchial  arches.  The  descending  branches  along  the  side  of  the  abdomen  are  spinal  nerves,  which 
escape  from  beneath  the  muscles,  and  pass  beneath  the  lateral  nerve,  but  do  not  communicate  with  it. 

FIG.  10.  Ganglion  of  the  sympathetic  nerve,  a,  trunk  of  the  third  spinal  nerve ;  i,  muscular  and 
cutaneous  portion  ;  c,  branch  to  the  ganglion,  dividing  into  ascending  and  descending  filaments,  which 
become  separated  from  each  other,  and  inclose  ganglion  cells ;  <2,  d,  sympathetic  fibres,  which  extend 
through  the  ganglion,  in  passing  which  their  filaments  separate  and  include  ganglion  cells. 

s 

FIG.  11.  A,  olfactory  pouch  ;  B,  olfactory  nerve  ;  C,  olfactory  lobe  ;  D,  cerebral  lobes  ;  V,  V,  orbitar 
branches  of  the  trigeminus,  crossing  the  olfactory  nerve,  sending  filaments  to  the  olfactory  pouch,  and 
terminating  in  the  skin  of  the  upper  lip. 


PUBLISHED    BY    THE    SMITHSONIAN    INSTITUTION, 

WASHINGTON,    1).    C.  , 

MARCH, 1853. 


PI.  I 


AdTiat     del     J   Wpna 


PL  II. 


in 


n»t.  d>l.  J.  Wyma 


